‘Simply Make a Change’—Individual Commitment as a Stepping Stone for Sustainable Behaviors

Abstract

In the face of climate change and other environmental issues, all relevant stakeholders, including members of civil society, should participate in the transformation towards a sustainable future. The project ‘Simply make a change’ engaged citizens (n = 101), with the help of an entirely voluntary and individual commitment approach, in a sustainable behavior they had not carried out before (e.g., plastic-free shopping or vegan nutrition). With the help of two questionnaires and subsequent interviews, participants were asked about their experiences with the commitment. The high proportion of participants who voluntarily sustained their chosen activity after the one-week trial run (78%), their rich and differentiated comments, and the formation of competencies such as mindfulness, reflectivity, and feelings of responsibility indicate that the approach was meaningful. Participants would have preferred a longer trial and perceived restrictions in daily life by behaviors with high task-difficulty (vegan nutrition), but felt confident to try out other sustainable behaviors in the future. The present data indicate that a completely voluntary self-commitment can encourage citizens to try out a new behavior and might also lower the threshold for trying other sustainable behaviors. This might contribute, step by step, to a more sustainable society.

1. Introduction

The world population is currently facing major environmental challenges such as climate change, air and water pollution, an increasing loss of biodiversity, as well as overconsumption [1,2]. In parallel, concerns about the impact of humans on the environment have increased substantially in the past decades [3,4]. Today, many people are aware that transformations towards a sustainable future are needed [5,6,7]. In the most recent environmental awareness study in Germany, broad sections of the population felt that more should be done for environmental, nature, and climate protection [5]. However, as in the preceding studies, a gap between environmental attitudes and individual environmental behavior was evident in all socio-economic groups [5]. Numerous studies have shown that mere concern and knowledge about the state of the environment is often insufficient to induce behavior change, even when individuals hold pro-environmental attitudes (e.g., [5,6,8,9,10]). Attitude-behavior gaps can be rooted in a lack of ideas and practical suggestions on what to do and the impression of struggling alone [9], high personal costs and low environmental benefits [6,11,12,13], situational constraints [14], or could be due to unsustainable habits [9,15]. One promising approach to promote environmentally friendly behavior in the short- and long term are commitment pledges that focus on the development of action skills or the execution of a desired behavior [3,16]. In the present study, citizens were encouraged with the help of an entirely voluntary self-commitment, which they had confirmed in writing, to engage in sustainable behaviors they had not carried out before. Evaluation of the project focused on both short- and long-term outcomes of the commitment and on moderating factors such as the type of behavior and its perceived difficulty.

1.1. Commitment as a Tool for Behavior Change

Commitment is a strategy to achieve self-set goals, and can be defined as the binding of an individual to a behavioral act [17]. Those who commit themselves to something declare that they will change a specific behavior for a certain amount of time (e.g., biking to work for a week instead of taking the car, or trying a vegan diet [18]). Commitments can be carried out alone or in groups and have been proven successful, even though the method stimulates behavioral changes with moderate rather than hard interventions [18,19,20,21,22]. Individuals, who want to engage in pro-environmental behavior such as reducing their energy consumption or buying organic food, are often not hindered by financial or situational barriers in doing so. In this case, they could make a resolution to change their behavior at some point, as it is often done at the turn of the year. However, a mere pledge might not result in sustainable actions. Due to, for instance, a lack of time or due to habit, people may quickly revert to their old behavior. Making a commitment publicly means that others, at least the organizers of the project, are aware of the commitment. This might increase a person’s injunctive norm (i.e., the extent to which he or she thinks that others are aware of the commitment and expect changes in the chosen behavior [23]). Injunctive norms have been found to be positively related to behavioral change (e.g., [24]).

Self-commitments have been shown to be more successful than incentive-based techniques [25]. Even highly attractive incentives rarely lead to lasting behavior changes since they do not allow individuals to find their own reasons for the behavior they perform [26,27,28]. Green nudges can also be an option to help people to adopt a new sustainable behavior, but were found to be more successful when combined with a commitment pledge [29,30,31]. When, for instance, more than 5500 British citizens received a nudge for climate-friendly diets, meal order intentions for low-carbon diets increased compared to an untreated control group. However, when people were subsequently encouraged to make a written commitment to climate-friendly diets, the effectiveness of the intervention increased by 90 percent [31]. Today, self-commitments are often used in the business sphere (e.g., [25,32,33], but there are also examples from schools and universities [34,35]). It should be noted that the obligatory fulfillment of pledges in the educational system could be understood as a kind of manipulation [18]. However, when Australian students had to make pledges as part of a university course, the self-commitment was not perceived as indoctrinating but as an eye-opening and valuable experience [36].

In a novel approach, the present study investigated the outcomes of a voluntary self-commitment, which was unrelated to the business sphere or the educational system. We expected that the self-commitment would help individuals to overcome barriers to pro-environmental actions (i.e., the lack of practical suggestions on what to do [9] or unsustainable habits [9,15]). As participation was made public, we expected that even an individual commitment might result in feelings of collective efficacy (i.e., the feeling that even more difficult tasks can be solved when not struggling alone [37]). We also expected that the voluntary participation helped people to bring their attitudes in line with their chosen behavior [19], resulting in positive feelings towards the tested activities, and attitudes such as mindfulness and responsibility. However, several factors might moderate the outcomes of a commitment approach.

1.2. Moderating Factors

The low-cost hypothesis predicts that low behavioral costs will have the greatest impact on environmental conduct, while high behavioral costs (i.e., if the action involves high financial expenses, much time or effort, can hinder environmental action) [6,11,38]. It can thus be assumed that the outcome of a commitment intervention depends on the perceived difficulty of the intended behavior. When, for instance, Swiss citizens had to rate various pro-environmental actions according to attributed execution difficulty, actions that needed little personal effort or caused little costs (e.g., glass recycling) were considered easy, while actions that involved high personal effort or costs (e.g., the installation of solar panels) were considered difficult [39]. However, there were several actions in the middle range of perceived difficulty that seemed hardly more difficult than the easy ones (e.g., turning off the light or heater when leaving a room for a longer period of time). Such difficulties are most likely grounded in habits [40]. Habits shape an estimated 35 to 50 percent of all human behaviors [15]. Habits make everyday actions easier, since they often take place unconsciously without a lot of effort [12,40]. If habits are to be discarded or transformed, a great deal of (mental) effort is usually required [41]. Behaviors that have become a habit, may be difficult to overcome, even if the alternative would be easy.

To investigate whether the success of a self-commitment is associated with the behavioral costs involved, the present study included activities with different levels of execution difficulty (as outlined in Section 2.2). We predicted that activities with high behavioral costs such as reducing car use and eating less meat or animal products might be more difficult to conduct than behaviors such as energy saving [42,43,44]. Moreover, they might be carried out less often.

1.3. Rationale of the Study and Research Questions

The main objective of the present study was to investigate whether a voluntary, individual commitment can support citizens in adopting and internalizing new sustainable behaviors in daily life. Totally independent of one another and of a certain location, interested persons were able to register online for the voluntary commitment, and thus make their commitment public. To our knowledge, this approach has rarely been used before. Previous research has either included fixed groups of people (e.g., the EcoTeam program [20]) or worked with pre-selected members of the public [18,19].

Research on commitment approaches has often looked at energy saving (e.g., [20,41,42,45]), and car-free mobility [22,46]. The present study included behaviors, which have recently received considerable attention in Germany, especially among younger people, such as plastic-free shopping, vegan nutrition and plogging, i.e., a combination of waste collection and jogging [37,47,48]. Moreover, while previous research has often focused on one behavior, we were interested in the evaluation of different behaviors with different degrees of execution difficulty, e.g., energy saving (easy) versus vegan nutrition (difficult). Following the recommendations by [38], we broke down sustainable behavior in different behavioral settings, i.e., household, consumption, nutrition and mobility behavior. The following questions guided the research:

Q1: How often and for what reasons were the individual behaviors chosen, how intensively were they carried out, and how difficult were they perceived to be?

Q2: What were participants’ experiences with the commitment and their chosen behavior?

Q3: How did participants evaluate the outcomes of the individual commitment directly after a one-week trial run and one month later, and did outcomes differ among the eight behaviors which could have been chosen?

Q4: How did participants perceive the self-commitment program two months after the commitment week?

2. Materials and Methods

2.1. Overview

In 2018, the project ‘Simply make a change’ aimed to encourage volunteers to execute a sustainable behavior for at least one week. The project was designed by the authors of this article. To advertise the project and to announce the online registration, various email distributors and the social networking website ‘Facebook’ were used. Moreover, Friends of the Earth Germany and the ‘District Future—Urban Lab’ of the Karlsruhe Institute of Technology (KIT) helped to distribute the project invitation via their own information channels. We expected to reach at least several hundred persons with the announcements of the project.

Interested citizens could choose one of eight behaviors. In order to bring about change, they were asked to select a behavior that they had not yet performed, and, if possible, to conduct it on a daily basis. On a website designed for the project, information about the project and detailed instructions on how to carry out the commitment was provided. Moreover, an online discussion forum offered opportunities for an exchange of ideas and experiences. The outcomes of the project were investigated with the help of two questionnaires, one directly after the commitment week and the other one about one month later. Moreover, two months later brief interviews were carried-out with some of the participants.

Individuals who had signed-up for the project were informed in advance about the study design. This guaranteed that participants were aware that their commitment would be viewed by the researchers, which is regarded as a prerequisite for a successful outcome of the approach [49]. The written instructions served as a reminder of the commitment. A reminder can make a commitment more significant, which in turn can lead to increased likelihood of sustained behavior change [19].

2.2. Selection of Behaviors

In a pilot study in 2017, randomly selected passers-by in the city of Karlsruhe were asked to rate 50 sustainable behaviors by perceived execution difficulty (on 5-step scales, ranging from 1: action is easy for me to 5: action is difficult for me). Several of the 50 behaviors were taken from a comparable study [50] after a careful examination of their current relevance. In addition, other—more trendy—behaviors such as vegan nutrition were included. 176 people filled-out the pilot questionnaire. The full set of behaviors ranked by rating scores can be assessed in Appendix A.

Out of the 50 behaviors, six were initially chosen for the present investigation. They represented different degrees of task difficulty (easy, moderate, and difficult), were effective in their environmental impact and also challenging without overwhelming the participants. Vegan nutrition and car-free mobility were chosen as difficult behaviors (mean scores of 4.9 and 4.2, respectively, on the 5-step scale), product checks with the help of apps and plastic-reduced shopping as moderately difficult ones (means of 2.7 and 2.6), and shopping of organically-produced food (mean of 2.1) and items related to energy saving (means between 1.4 to 2.1) as rather easy actions (see Appendix A). Plogging and the production of natural cosmetics and detergents for personal use were later on included in the final set of behaviors since they recently had received much public attention in Germany. Moreover, plastic-reduced shopping was changed to plastic-free shopping to make it more challenging.

In order to cover a variety of interests, the eight behaviors were from different subject areas, i.e., consumption and nutrition (organically-produced food, vegan diet), health (product checks with apps, production of cosmetics/detergents), energy and mobility (energy saving, car-free mobility) and waste (plogging, plastic-free shopping). With regard to the more difficult behaviors, a commitment period of one week with the option to continue with the new behavior for at least one more month under project conditions was considered appropriate.

2.3. Project Website

A project website contained detailed information on each of the eight behaviors. All relevant information was summarized in a document that could be downloaded from the website. The website provided a wealth of information about the project, was enriched with many illustrations, and had a user-friendly handling (https://mitmachprojekt.wordpress.com/das-projekt/umweltfreundliche-verhaltensweisen/, accessed on 20 June 2023). During the course of the project, the number of participants and types of commitments performed were registered and updated daily. Participants could refuse these anonymous entries on the website when registering. However, only 3% did so. A discussion forum offered the opportunity to exchange ideas with other participants, but was rarely used (only by ten persons). The resulting discussion was moderated by the project leader and questions that arose were answered. Nevertheless, users welcomed the opportunity to exchange ideas in the forum.

2.4. Registration, Ethical Considerations and Questionnaires

The registration form and the two questionnaires were created using the online survey tool SoSciSurvey. The registration was understood as a kind of virtual contract [51]. Participants could also provide their email. In this case they received a reminder when a questionnaire had to be answered. To ensure anonymity, all email addresses were stored separately from the collected data. They were used exclusively for the study and deleted after all data had been collected. An identification code guaranteed that both questionnaires, and later-on also the interview, could be assigned to the same person. Registration was possible over a period of three months. During this time, 103 people had declared their willingness to make a voluntary commitment.

On the website of the project, participants were automatically informed about the privacy policy when registering. In order to comply with the principles of ethically responsible handling of research subjects, of collected documents and of data, participants were informed about the research objective and the research methods. They were assured of anonymity (confidentiality, anonymity in publication), and that they could revoke their data at any time.

In the first questionnaire, experiences with the one-week commitment were investigated. Participants were asked which behavior they had chosen and for what reasons, how often they had carried it out (in days), and how difficult it was to execute the behavior (5-step scale from 1: easy to 5: difficult). They also assessed the suitability of the commitment duration of one week (5-step scale from 1: too long to 5: too short). In two open questions, participants were invited to provide information on their positive and negative experiences with the commitment week. Moreover, they were asked about their opinion on eight statements related to feelings and actions during the commitment week (on 5-step Likert-scales, from 1: disagree to 5: agree; statements in Table 5). To avoid an influence of item content on participants’ free associations with the commitment, statements were shown after the comments had been provided. In addition, age, sex, and place of living (to be indicated on a 5-step scale, ranging from 1: rural to 5: urban) were recorded. These variables were found influential on pro-environmental behavior. For example, women have been found to be more concerned about the environment than men, and also more likely to engage in environmentally friendly behaviors [38]. Moreover, car-free mobility was more difficult for people living in the countryside than for those living in urban regions [39], which could also be true for most of the other behaviors examined in the present study.

In the second questionnaire (one month after the commitment week), participants were asked whether they had continued with their chosen behavior and, if so, on how many days, and whether they considered the continuation difficult (5-step scale, from 1: easy to 5: difficult). In an open question, participants were asked to write down why it was easy or difficult for them to integrate their new behavior into everyday life. Moreover, they were asked with the help of 5-step Likert scales (from 1: disagree to 5: agree) about their opinion on various experiences with the new behavior (see statements in Table 5). Finally, participants were asked whether they would be willing to take part in a subsequent interview. In this case, they had to provide an e-mail address which was solely used for this purpose.

2.5. Interviews

Brief interviews were carried out two months after the commitment week. Interviewees were asked whether they had carried on with their chosen behavior and, if so, for what reasons. They were further asked to describe their impressions of the whole project and their personal insights and experiences. Finally, some key results of the two surveys were presented and interviewees asked to compare the results with their own experiences.

Initially, 42 people had agreed to be interviewed and thus provided an e-mail address. Of those, 18 were finally chosen, representing the eight different behaviors in roughly the proportions in which they had been chosen by the participants. Since the interviewees lived in different regions of Germany, all interviews were conducted by phone.

2.6. Participants and Data Analysis

Of the 103 persons originally registered, 101 eventually participated in the survey. The response rate to the first questionnaire was 77% (n = 78) and to the second one 62% (n = 63). Participants (83% women) were between 20 and 76 years old (mean = 34 years, SD = 13.7). About 17% of participants were from a rather rural, 10% from neither a rural nor an urban, 18% from a rather urban and 55% from an urban area (mean urbanity = 4.1 on the 5-step scale, SD = 1.26).

Text entries for the open questions were evaluated with MAXQDA 11, using inductive category formation [52]. The category system was twice cross-checked by two other persons, resulting in an intercoder reliability of 91%. Comprehensibility of the questionnaires was tested in a pilot study with ten people. After feedback had been received, some questions had to be re-phrased. Trial interviews were conducted with two people. A brief analysis of the interviews with deductive-inductive category formation was carried out with MAXQDA 11.

Multiple linear regression with backward elimination of non-significant variables (p > 0.05) was used to test for a relationship between commitment intensity (total number of days on which a behavior was carried out during and after the commitment week) and mean execution difficulty (scores), age, sex and type of place of living (mean urbanity). As this type of analysis does not allow strong correlations between explanatory variables (r > 0.35), Pearson correlations between binomial and metric explanatory variables were tested first. However, none of the explanatory variables were strongly correlated with each other.

With the help of eight items (see Table 5), the experiences of the participants with the commitment and new behaviors were investigated. To obtain overall scores of participants’ satisfaction, the eight individual scores obtained during and after the commitment period were each summed up. Since in two of the items lower scores indicated higher satisfaction (the last two items in Table 5), they were substituted by their complements (i.e., 6 minus score; e.g., 5 → 1). Differences in overall satisfaction between the eight behavior groups with the commitment during and after the commitment week were tested by analyses of variance. Multiple linear regressions were then used to test for relationships between overall scores and commitment intensity (number of days on which a behavior was carried out during and after the commitment week), perceived implementation difficulty (during and after), age, sex, and urbanity. The final minimum adequate models were obtained by backward elimination of non-significant (p > 0.05) variables. All analyses were carried out with SPSS for Windows 29.0.

3. Results

3.1. Choice of Behavior, Frequency of Implementation and Perceived Difficulty (Q1)

Among the eight behaviors, plastic-free shopping and vegan nutrition were most frequently chosen (

Table 1. Frequency of execution of the eight behaviors (mean number of days) and perceived execution difficulty (on 5-step scales from 1: easy to 5: difficult). Participants provided information for the commitment period and the following month. In brackets: number of participants who had signed in for a certain behavior/number of participants who provided information in both questionnaires.

Behavior	Mean Days of Execution			Perceived Difficulty (Mean Scores ± 1 SE)
	Commitment Week (7 Days)	Afterwards (30 Days)	Overall (# Days)	During Commitment	After Commitment	Overall Mean
Plastic-free shopping (27/16)	5.4	12.5	18.2	3.4 ± 0.29	3.4 ± 0.20	3.4 ± 0.23
Vegan nutrition (21/11)	6.6	5.4	12.1	2.6 ± 0.28	3.7 ± 0.20	3.2 ± 0.21
Plogging (15/9)	4.6	5.7	10.7	3.1 ± 0.46	3.2 ± 0.32	3.2 ± 0.22
Energy saving (10/6)	5.3	16.0	21.8	2.8 ± 0.17	2.8 ± 0.31	2.8 ± 0.17
Product check with Apps (9/6)	4.2	3.0	7.2	2.2 ± 0.31	2.8 ± 0.48	2.5 ± 0.29
Organic food consumption (8/5)	5.6	8.8	14.4	3.2 ± 0.37	2.8 ± 0.20	3.0 ± 0.27
Car-free mobility (6/4)	6.8	14.3	21.0	2.5 ± 0.50	2.5 ± 0.29	2.5 ± 0.35
Cosmetic/detergent production (5/4)	4.3	15.0	18.3	2.3 ± 0.25	3.0 ± 0.41	2.6 ± 0.31

). Participants chose a behavior since they regarded it as a challenge (59%), always had wanted to try it out (51%), and felt confident to succeed (44%).

About 42% of participants considered the commitment duration of one week just right, while 58% felt that it was (rather) too short. On average, a behavior was carried out on 5.3 days during the commitment period and on 9.7 days in the following month. However, there were differences between the behaviors. While car-free mobility and vegan nutrition were frequently performed during the commitment week, product checks were less often carried out (see Table 1). In the month following the commitment week, behaviors such as energy saving, the production of cosmetics/detergents and car-free mobility were rather frequently conducted, while product checks or vegan nutrition were only rarely carried out.

Among the eight behaviors, product checks were considered easiest and plastic-free shopping the most difficult to carry out during the commitment week (see Table 1). However, none of the behaviors was perceived as (rather) difficult. One month later, assessments for most behaviors had hardly changed. Vegan nutrition, however, was then perceived as much more difficult (increase of more than one score). Perceived difficulties during and after the commitment week were positively correlated (Pearson correlation coefficient = 0.30, p = 0.018).

In the multiple linear regression model, the total number of days on which a behavior was carried out was negatively related to mean perceived execution difficulty (b = −4.29, t = −3.01, p = 0.004) and influenced by sex (b = 10.95, t = 3.37, p = 0.002). With increasing execution difficulty, the commitment was fulfilled during fewer days. Moreover, men spent almost eleven days more on the commitment than did women.

3.2. Experiences with the Commitment and the Eight Behaviors (Q2)

About 98% of all respondents provided a comment in the first and 79% in the second questionnaire. All participants reported positive experiences during the commitment week, which could be sorted into three main categories. Many statements referred to a sense of achievement or, not mutually exclusive, sense of competence such as awareness and mindfulness, action competence and reflection, and some referred to the method itself (

Table 2. Positive experiences during the commitment week in view of 77 participants. Multiple answers were possible. Answers to the open question were sorted into broad categories. In brackets: number of participants (bold), number of responses (italic), m = man, w = woman, age in years, chosen behavior.

Categories/Subcategories	Examples
Personal Experiences (n = 65)
Sense of achievement (54)	Saving electricity is actually very easy. The project week helped me to put it into practice, and there is no good reason to stop it now (w, 64, energy saving).
Exchange with others and multiplication effect (13)	Many discussions about my topic have emerged and stimulated me and others to make lasting changes (w, 40, organic shopping). I was able to motivate neighbors and friends to participate in the collection of garbage (w, 37, plogging).
Motivation and challenges (13)	I am motivated to make lasting changes (w, 22, organic shopping). I found it challenging that I always had to take the bike (m, 39, car-free mobility).
Enjoyment and satisfaction (12)	It was fun to deal more consciously with my diet (w, 26, vegan nutrition). The more days I collected, the cleaner my walk became—and still is—and I am happy (w, 56, plogging).
Capacity building (n = 61)
Awareness and mindfulness (39)	Participation has increased my awareness. Not just for energy saving, but generally for sustainable behavior (w, 21, energy saving). Attention has been drawn to small things that are harmful to the environment and which you would otherwise not notice (m, 24, car-free mobility).
Action competence (28)	I will continue to reduce my plastic consumption (w, 23, plastic-free shopping). Organic milk was always sold out and I finally complained about it. I had a nice conversation with the shop manager that will change his ordering behavior permanently (w, 40, organic shopping).
Reflection (21)	The commitment has shown me that it is often possible to use a bike. Most of the time, habit is the reason to use the car (w, 31, car-free mobility). I might only have used energy a bit less, but if we would all do it consistently, we could certainly shut down some power plants (w, 64, energy saving).
Obtaining information (16)	Researching and collecting information was stimulating. I wrote down which products are wrapped in plastic and which I actually do not need (w, 30, plastic-free shopping).
Planning and self-control (6)	I need to pay attention to little things: always have my own spoon and a box with me when ordering ice cream or taking leftovers from a restaurant (w, 22, plastic-free shopping).
Feeling of responsibility (4)	I got a feeling of responsibility for my environment through these small actions (w, 27, plogging).
Methodology (n = 38)
General insights (24)	I think we should often spend a week like this to remind ourselves of certain values, to constantly increase awareness and to try out new things. I am sure that every time something will stick (w, 26, organic shopping).
Initiation of behavior (13)	I have finally done things that I have wanted to do for a long time (w, 76, energy saving).
Transfer to other topics (8)	I got ideas for other possible commitments, several of which I find very interesting (w, 29, energy saving).
Sense of duty (6)	The commitment is voluntary, but you have to report on it after a week. This gets you going (m, 26, plogging).

).

Participants had also encountered difficulties (reported by 72 persons). Most often, they were of a general nature. Some participants had reverted to old habits, felt restricted by their behavior or expressed a wish for a longer commitment period (

Table 3. Negative experiences during the commitment week in view of 72 participants. Multiple answers were possible. Answers to the open question were sorted into broad categories. In brackets: number of participants (bold), number of responses (italic), m = man, w = woman, age in years, chosen behavior.

Categories/Subcategories	Examples
Obstacles (n = 66)
General difficulties (40)	I quickly gave up on my walk next to the train tracks, because of the huge amount of rubbish lying around; some things were just too nasty to pick up (w, 27, plogging).
Old habits (21)	In many situations, one tends to forget the voluntary commitment out of habit. The tasks really need to be made consciously, which is quite an effort (man, 32, energy saving).
Restrictions and sacrifices (18)	We could not buy things we actually needed as they were not plastic-free (m, 63, plastic-free shopping). In some situations you cannot eat when no vegan food is on offer (m, 30, vegan nutrition).
Time constraints (10)	I detested the extra time it took me, and the delays and unpunctuality of public transport (w, 67, car-free mobility).
Lack of social acceptance (9)	I started to avoid crowds and stopped when I felt watched (w, 52, plogging).
Revelation (8)	I was aware of how ubiquitous plastic is. But during this week and in preparation for it did I realize how pervasive it is. I had the impression that there is almost nothing that is not wrapped up in plastic (w, 63, plastic-free shopping).
Financial constraints (8)	Since we did not shop at discounters, costs were greatly increased this week (w, 32, organic shopping).
Methodology (27)
Project duration (17)	The commitment should be for a little longer so that the new behavior can become a routine (w, 31, product checks).
Relevance and impact (5)	I question the relevance and impact of my doings (m, 26, plogging). I have not used a hair-dryer. I might not keep up such small activities as they have so little impact (w, 29, energy saving).
More information (5)	Links to interesting websites would have been stimulating and helpful (w, 22, plastic-free shopping).

).

One month later, participants reported that they had experienced personal limitations and other difficulties, but had also fallen back into old habits. On the positive side, they emphasized that their new behavior had become an integral part of everyday life and that awareness of sustainability had been fostered (

Table 4. Experiences in the month following the commitment period in view of 63 participants. Multiple answers were possible. Answers to the open question were sorted into broad categories. In brackets: number of participants (bold), number of responses (italic), m = man, w = woman, age in years, chosen behavior.

Categories/Subcategories	Example Statements
Barriers (46)
Sacrifices, old habits and routine (37)	It is very difficult for me to do without cheese and right now, during barbecue season, meat simply tastes too delicious. It is certainly a habit (w, 30, vegan nutrition). You quickly return to routine; a week is too short for changing a behavior (w, 27, plastic-free shopping)
Situational, time and financial constraints (19)	I plan to go back to nature armed with bags, but unfortunately, I have not found the time in the past four weeks. In my opinion, jogging is less of an option, because then it is actually only collecting instead of jogging. There is simply too much garbage everywhere—very frightening (w, 37, plogging). Living in the country, you have to plan a lot because you have to go into town—and the items are more expensive than the ones you can buy in the local supermarket—and not necessarily better (m, 63, plastic free shopping).
Successes (39)
Increased consciousness and changes of habits (39)	Environmentally-friendly behavior is actually a matter of mind and awareness—and often the overcoming of comfortable or accustomed behavior. If you realize that, it will help to correct things—and you will be rewarded with small success stories (w, 77, energy saving)

).

When comments were analyzed separately for each behavior, type-specific characteristics became visible which will be illustrated in the following. Only statements from persons who had answered both questionnaires (n = 61) are included.

Plastic-free shopping (16 persons): Most often, experiences of success (#12) and an increased sensitization for the topic (#10) were mentioned. Participants also realized that many products cannot be bought without plastic (10 persons each in questionnaire 1 and 2).

“It is not that difficult to improve your behavior towards the environment. Often, there is a plastic-free alternative or at least one with less plastic. I could not find some things plastic-free, e.g., toilet paper, cottage cheese, curd cheese, paper tissues.” [...] One month later: “It is easy for me if there is a plastic-free alternative or if I have to make slight compromises. In this case, I buy the plastic-free product. It is difficult for me if I cannot get certain products plastic-free or have not yet found them. [...] I cannot do without some of these products; I do not want to do without some” (woman, 63 years old).

Vegan nutrition (11 persons): During the commitment week, respondents most of all wanted to eat healthier or try out new products and recipes (#9). Only two missed cheese or other things. One month later, however, many participants felt rather restricted since they could not eat the things they like or could not join friends or colleagues for lunch or dinner (#8).

“I did not really perceive it as a sacrifice, since I treated myself to a lot of things that I do not usually buy (e.g., various vegan spreads, special types of tofu). I also made vegan spreads myself—it was not difficult, because there are now many vegan products available.” One month later: “In some situations you are excluded and cannot eat when the offer is not vegan” (man, 30 years old).

Plogging (9 persons): Participants liked the direct feeling of success (#8), but disliked the reactions of other people (#5; only mentioned in questionnaire 1). Picking up waste was sometimes perceived as disgusting (#3), but some participants explicitly mentioned that they had nothing negative to report (each three in questionnaire 1 and 2).

“I liked the fact that I felt bound by the commitment and that I was less able to shirk the “work”. Basically, I am reluctant to clean up other people’s rubbish as I myself do not leave anything outside a dustbin or take everything home again. I belong to the “good guys” and have no behavior to change. That is why I believe that my civic engagement makes it too easy for the perpetrators. Personally, it has been a huge problem for me to collect garbage in front of everyone.” One month later: “Although the discussion among colleagues was quite controversial, I am surprised that I believe I can make a difference (role model function) and that I feel good about it (better than complaining about the dirt)” (woman, 61 years old).

Energy saving (6 persons): Participants had always wanted to do it and were happy to put it into practice (#4). Main obstacles were habits and routine (each three in questionnaire 1 and 2).

“I finally did things I had actually wanted to do for a long time: bought and installed new LED lamps; replaced the old so-called energy-saving lamps, which had annoyed me long enough because they took so long to get bright. While thinking about the possibilities, I realized that I automatically switch on the light in the cellar even in broad daylight. [...] I have noticed how deep-rooted many things are and how much effort is needed to stop bad behavior and habits.” One month later: “Actually, I would not find it difficult if it was not for the convenience. [...] Environmentally-friendly behavior is actually a matter of mind and awareness and of overcoming comfortable or habitual behavior. If you are aware of this, it helps you to correct some things and you are rewarded with small feelings of success” (woman, 29 years old).

Product checks with apps (6 persons): All participants had shopped more consciously during the commitment week, but some wanted further information (#3). One month later, most were still motivated to use the app, but not on a regular basis (#4).

“I really enjoyed taking a closer look at the products I buy. It is a great idea to rethink your habits and see how you can change something in your everyday life. I expected more information from the app. I thought that there might be some information regarding different labels.” One month later: “It is easy for me because I hardly buy products that contain environmentally harmful substances. I can check those that are questionable which applies especially to cosmetic products or detergents” (woman, 24 years old).

Consumption of organically-produced food (5 persons): Directly after the commitment week, all participants reported a more conscious purchase of groceries and an increased awareness of sustainability. However, four of them also mentioned the high amount of plastic packaging. One month later, all participants were rather willing to carry on with their chosen behavior, although some products could not be bought or were too expensive (#3).

“You buy more consciously and purposefully and not mass products. Many organic products are packaged in plastic, which in my opinion is a big contradiction.” One month later and continuing the behavior: “Because I think it is important not only to talk about sustainability, but to live it” (man, 35 years old).

Car-free mobility (4 persons): Participants were proud to leave their comfort zone, but either liked biking already or lived in an environment with good public transport (mentioned in all comments).

“I paid more attention to my daily planning and time management. I like the sporty aspect of moving around by bike. I became more confident in dealing with timetables and public transport. Negative were the extra time to carry out the commitment and the delays of public transport.” One month later: “Since I have always liked to ride a bike, I have done it now more often (instead of using the car). I am also now more familiar with public transport and feel confident to get around without a car. The environmentally-friendly behavior gives me the good feeling of doing something for climate protection and health” (woman, 62 years old).

Cosmetic/detergent production (4 persons): Participants provided joyful comments on the production process (#4 in questionnaire 1), but also said that it would take a lot of time (each 3 in questionnaire 1 and 2).

“I made soap myself. It has to mature for six months. I also made dishwashing liquid—that works great. I have also prepared the vinegar cleaner. It has to soak for at least two weeks. [...] One week is too short. It takes at least a year to make your own cosmetics—you have to find out where to find the materials, the recipes” [...]. One month later: “You have to plan in advance to have detergents ready when you need them” (woman, 34 years old).

3.3. Evaluation of Commitment and Behavior (Q3)

In both questionnaires and with eight corresponding statements, participants were asked about their feelings and actions during and after the commitment week (statements and mean agreement scores in

Table 5. Evaluation of commitment and behavior. With the help of eight corresponding items, participants stated their opinion (5-step scales, ranging from 1: disagree to 5: agree) on the commitment week/the following month. Only persons who had answered both questionnaires were included in the analyses (n = 61).

Statements (Questionnaire 1/Questionnaire 2)	Mean Score ± 1 SE
	During	After
I was happy to carry out the commitment//I still enjoy carrying out my behavior	4.6 ± 0.14	3.9 ± 0.14
I was motivated to successfully implement the commitment/I am motivated to carry on with my behavior	4.4 ± 0.10	4.1 ± 0.13
I see the commitment/my behavior as an important contribution to environmental protection	4.4 ± 0.10	4.4 ± 0.10
I talked to other people about my commitment/during the last weeks I have talked to other people about my behavior	4.4 ± 0.13	4.1 ± 0.14
The commitment made me feel that I could make a difference through my environmentally-friendly actions	3.9 ± 0.14	3.7 ± 0.15
During the commitment week I came up with more ideas …/… the last weeks I have realized ideas for an environmentally-friendly lifestyle	3.5 ± 0.14	3.8 ± 0.15
I felt restricted in everyday life by my commitment/I feel restricted in everyday life by my behavior	2.8 ± 0.15	2.8 ± 0.15
I had to give up things due to my commitment/I have to give up things due to my behavior	2.7 ± 0.17	2.6 ± 0.17

; agreements sorted by behavior in Figure 1).

Enjoyment: Participants were happy to carry out the commitment (highest mean score; Table 5). They still enjoyed their behavior one month later, but to a lesser extent. The largest decline was observed in vegan nutrition (about two scores less on the 5-step scale; Figure 1a). Plogging was only moderately enjoyed, both during and after the commitment week.

Motivation to succeed: Persons who had chosen organic food consumption, car-free mobility, cosmetic/detergent production or plastic-free shopping were especially motivated to successfully implement the commitment and to carry on with their chosen behavior (mean scores > 4.4 on the 5-step scale; see Table 5). As with enjoyment, agreement scores for vegan nutrition strongly declined after the commitment week (Figure 1b, compare Figure 1a).

Contribution to environmental protection: Both during and after the commitment week, participants rather agreed that their commitment and chosen behavior will contribute to environmental protection (mean scores > 3.8 on the 5-step scales; Figure 1c). In most cases, scores remained constant or even increased one month later.

Communication: Participants stated that they had talked with others about their commitment and behavior, especially those who had committed themselves to plastic-free shopping (see Table 5; Figure 1d). For vegan nutrition, product checks and plogging, agreement scores declined after the commitment period, while they strongly increased for car-free mobility.

Making a difference: Persons, who had committed themselves to car-free mobility, plastic-free shopping or cosmetic/detergent production were most sure that they could make a difference through their environmentally-friendly actions (mean scores > 4.2 on the 5-step scale), while those who had committed themselves to vegan nutrition, product checks or plogging were least sure (mean scores between 3.0 and 3.6; Figure 1e).

Additional ideas: In the second questionnaire, compared to the first one, participants more strongly agreed that they had come up with additional ideas for an environmentally-friendly way of life (see Table 5). There was an increase in the feeling to have come up with additional ideas, most strongly in organic food consumption, product checks and vegan nutrition (Figure 1f).

Restrictions in everyday life: By their commitment and chosen behavior, participants felt moderately restricted in everyday life (see Table 5). After the commitment week, feelings of restriction increased for those participants who had chosen vegan nutrition, energy saving or car-free mobility, but decreased for all other behaviors, most strongly for organic food consumption and product checks (Figure 1g).

Sacrifices: Participants who had committed themselves to vegan nutrition thought that they had made sacrifices (Figure 1h). This was also the case for organic food consumption during the commitment week, but hardly afterwards (mean scores of 3.6 and 1.8, respectively).

Across all statements, a maximum score of 40 could have been reached (eight items, always strongest agreement on the 5-step scale; in case of restrictions and sacrifices scores were adjusted). Mean scores were 32.0 ± 0.56 in the first and 30.6 ± 0.71 in the second questionnaire. In the first questionnaire, scores did not differ significantly between the eight behaviors (F7,53 = 1.16, p = 0.344). In the second questionnaire, however, differences were found (F7,53 = 4.21, p = 0.001). A commitment to vegan nutrition received the lowest overall score (25.0), while a commitment to the production of cosmetics/detergents received the highest one (36.0).

In the multiple linear regression models, overall scores were positively related to the number of days on which a behavior was carried out (during commitment: b = 0.93, t = 2.44, p = 0.018; one month later: b = 0.32, t = 3.17, p = 0.003). Moreover, women agreed more strongly with the statements in the first questionnaire than did men (b = 4.00, t = 2.08, p = 0.042).

3.4. Impressions Two Months Later (Q4)

With one exception, interviewees (n = 18) had continued with their behavior and established some routine. They were sure that the project had fostered awareness and action competence, and disagreed with the need for a longer commitment period (

Table 6. Reflections about the commitment two month later. Interviews were carried out with 18 selected persons who had participated in both questionnaires. Statements were sorted into broad categories. In brackets: number of responses, m = man, w = woman, age in years, chosen behavior.

Categories	Examples
Increased awareness and action competence (18)	Yes, I think mindfulness already plays a role. I think twice—do I really need it now, is it just convenience or what motivation do I have to use the car (m, 39, car-free mobility). It is important that we as customers communicate to shops and manufacturers that we want alternatives, that we want plastic-free products. I cannot understand why recycled toilet paper has to be wrapped up in plastic. I wrote that to a health-food store. If the manufacturers adjust to this, a lot can be achieved, much more than trying to change something as an individual (w, 62, plastic-free shopping).
Sensitization for sustainable actions in general (3)	It is not only saving electricity, but when you become aware of one thing, you also think about completely different things. And little by little there are other habits. […] The coolest thing I really found was that the project spreads like a spiral into all other areas of life (w, 23, energy saving). You also pay attention to more difficult things and behaviors, and you already create a transfer (w, 41, organic shopping).
Erosion of behavior (17)	It does not work 100 percent but I do it as often as possible (m, 28, plastic-free shopping). As long as I could tell someone about the commitment week—this may sound silly now—I took it seriously. I still carry on with my behavior because I know that it is a good thing. But I think it will expire. That someday I will not do it anymore (m, 26, plogging).

). Some interviewees described a general sensitization for sustainable actions, which went beyond the topic of their chosen behavior. However, interviewees also argued that the willingness to conduct a certain behavior might erode over time.

4. Discussion

Several lines of evidence indicated that the project ‘Simply make a change’ was meaningful: the rich and differentiated comments, the answers to the statements, the high proportion of participants who voluntarily sustained their chosen activity after the official commitment period (78%), the number of persons who volunteered for an interview, and the interviews themselves. Participants were motivated and happy to carry out the commitment, which is an important condition for the continuation of a green behavior [53,54]. Despite the short duration of one month, participants felt confident to implement their new behavior in everyday life, perceived their actions as an important contribution to environmental protection, and wanted to try out other sustainable behaviors. The commitment had thus acted as a nucleus for change. This was also apparent in the formation of competencies such as awareness and mindfulness, action competence, reflectivity, planning and self-control as well as feelings of responsibility. These competencies are part of the concept of ‘Gestaltungskompetenz’, which is defined as the capacity of an individual to act and solve problems, and in doing so to contribute to a more sustainable society [16,55,56]. Similar competencies were fostered when teenagers participated in a collective public commitment and accompanying workshop on plastic consumption [18], exemplifying that both individual and collective commitment can strengthen the willingness and ability of individuals to take action.

Behaviors such as vegan nutrition, plastic-free shopping, and plogging were frequently chosen. They reflect the zeitgeist and are currently popular in Germany and elsewhere, especially among younger people [47,48,57]. However, these were also the behaviors that were perceived as rather difficult to perform. In this way, participants involuntarily took into account the recommendation to use challenging tasks for gaining success [23]. As predicted, vegan nutrition, a high impact behavior in terms of sustainability, required great effort from the participants in its implementation. It was the one behavior that was found to be most restrictive and leading to a loss of free choices in daily life as in [44,58]. In a consumption survey, people found it easier to consume plant-based meat alternatives in situations where one eats alone or with family than in formal situations [59]. Not surprisingly, vegan nutrition scored lowest in the project evaluation, and showed a noticeable decline in enjoyment, motivation, and number of execution days after the commitment week. Despite the observed difficulties, vegan nutrition did not have a higher dropout rate than the other activities. However, as the number of execution days and the overall satisfaction with the project was positively related, a longer commitment period would be advisable in future projects.

In contrast to our predictions and recent research results [42,44], car-free mobility—like vegan nutrition a high-impact behavior [12]—was perceived as rather easy by the few individuals (n = 4) who had carried it out. However, according to their comments they were persons who already liked biking, which means that the threshold to practice car-free mobility was rather low. This was also the case for cosmetic/detergent production since participants seemed to love manual activities. The 27 participants, who had chosen plastic-free shopping, reported on the one hand that they had successfully changed their consumption pattern, but on the other hand that they had to realize that many products cannot be bought without plastic. This was also the case in a study where people tried to live plastic-free for one month [60]. A missing offer of plastic-free alternatives was by far the most important barrier for participants to purchase less products with plastic [60]. However, in the present study plastic-free shopping still had a relative high number of execution days, showing that the commitment had an effect. Experiences with plastic-wrappings were also reported by the eight participants who had committed themselves to organic food consumption. Although this activity was perceived as less difficult than plastic-free shopping, participants were likewise confronted with the realization that many products were wrapped-up in plastic. Unintentionally, participants became thus aware of other sustainability issues and behaviors that could be changed. Spillover effects (i.e., transfer to other sustainable actions when a sustainable behavior is already being performed) can occur between similarly difficult actions, but can also move toward more difficult ones to perform [61]. Spillover effects, but most of all action competence and the genuine effort to make one’s own behavior more sustainable, were frequently mentioned in the interviews two months after the project had ended. In a collective commitment study, even three years later all former participants had either retained their new behavior or replaced it with another one. In addition, they had familiarized themselves with other sustainable behaviors and in some cases already tried them out [18]. The present results indicate that even a commitment to practice a new behavior for only one week may result in both short- and long-term behavioral changes.

As in other studies on green consumption [62,63,64], high prices were a challenge for participants who committed to the purchase of organically produced food. However, as with plastic-free shopping, participants were still highly motivated to carry out their chosen behavior during and after the commitment, and did mostly not feel that they had made sacrifices (as shown in Figure 1). One reason could be that organic food consumption, and most likely also vegan nutrition, are strongly associated with underlying ethical values such as fairness and care [64,65], so that the perceived ratio of benefits to costs is higher. Energy saving was perceived as moderately difficult (as predicted) and characterized by relapses into old habits. However, due to frequent repetitions—energy saving was the behavior with the most repetitions anyway—habits might be discarded over time [12,41]. As already mentioned, the perceived difficulty of an action affects whether it will be carried out. In a Dutch study, a private commitment influenced energy saving behavior only when the behavior was perceived to be relatively effortful [21]. In this case, individuals felt morally obliged to engage in the behavior to which they had committed. This might explain, why product checks with Apps, which were perceived as rather easy to perform and hardly restrictive, were carried out less frequently than the other types of behavior and, according to the participants, will only be used irregularly in the future. Plogging was the one behavior with high environmental gain (clean environment), but weak personal gain (“just cleaning up other people’s rubbish”). In consequence, participants, who had chosen plogging, reported only moderate enjoyment and only moderate motivation to continue with the activity. This result is in line with the theory of planned behavior [23], which implies that individuals are more likely to behave in a certain manner if the behavior is beneficial to them. In Korea, where plogging is trendy among people aged 20 to 40, it is always carried out by larger groups and seen as a community event [48]. This gives participants the feeling that they are not fighting for environmental protection alone, but are part of a larger movement. It might therefore be advisable to integrate activities such as plogging into collective actions to allow for group reinforcement.

Although the online discussion forum was rarely used, participants reported a clear need to talk to others about the commitment. Most often they had exchanged their experiences with family, friends and colleagues. This was also the case in a collective commitment study. Here, young people enjoyed the group exchange, and also the exchange with family members, friends and other persons about their experiences with the behaviors to be tried out [18]. Recognition and encouragement from others can serve as mental support and provide a ‘warm glow’ (i.e., a reward for doing the right thing), which is considered a strong motivator for pro-environmental behavior [66,67]. Nevertheless, even without the exchange in a fixed commitment group, as in [18,20], participants felt empowered to make changes. However, in future self-commitments, social media could be used, as in [48], to connect at least those participants who would like to have more exchange in a group.

The total number of days on which a behavior was carried out during and after the commitment week was not related to a person’s age. Age was also not related to the overall evaluation of the commitment approach. This indicates that a self-commitment can be suitable for people of all ages; the oldest participant in the present study was 76 years old. It is also noteworthy that one-third of those over 50 had chosen plogging, which is usually more popular among young people. The tested variables were also not related to urbanity. Although there was a complaint about the unavailability of products in the countryside (see Table 4), it neither impacted commitment intensity nor the evaluation of the approach. Men invested more time than women in their change of behavior, but women seemed more satisfied with the outcomes of the commitment week. One reason could be that women are more concerned about the environment than men and also more willing to engage in pro-environmental behavior [38].

Study Limitations

Due to the small number of participants and the convenience sample, our results should be interpreted with caution. It should be noted that only between four and sixteen people have participated in a behavior. Moreover, the results are based on self-reports, which might not reflect actual behavior. In addition, a period of two months might be too short to conclude that participation in an individual commitment results in sustainable behavior changes. In the first month following the one-week trial run, the chosen behaviors were carried out for approximately ten days. In a British study, however, it took individuals about 66 days to carry out their new behavior as an automatic action [68]. A longer duration of the commitment period was also requested by 60 percent of the participants, and would have been an additional support. Participation in the present project was entirely voluntary. It is therefore possible that only individuals participated, who were already sensitive to environmental issues. Moreover, the project was advertised through information channels such as ‘Friends of the Earth’, which are very likely to be frequented by people with a high interest in sustainability. However, it is probably these people who want to make a difference, and it is therefore worthwhile to support their efforts. A striking feature was the imbalance between the number of participating women (83%) and men. One reason could be that the focus of the present self-commitment was more likely to appeal to women than men, as most of the targeted behavioral changes may have been associated with household activities such as consumption and nutrition, energy saving and plastic-free shopping. Several studies have shown that women are more likely to go green in the private sector, while men are more likely to go green in the public sector (i.e., become active outside the household) [69,70,71]. Moreover, females were found to display more concerns about animal welfare and the environment than did men [59].

5. Conclusions

What lessons can be learnt from the project? The project ‘simply make a change’ provided an impetus for interested citizens to put a long-standing behavioral intent into practice. It was successful in the formation of competencies that strengthened participants’ willingness and ability to take action. The online announcement worked well, and the scheduled trial run of only one week offered a low threshold for people who wanted to try out one of the more difficult behaviors such as vegan nutrition. However, follow-up prompts via the project website might be a useful future tool to support people in the continuation of their chosen behavior. Moreover, a longer commitment period would be advisable so that new behaviors have more chance to become a routine. The present results also exemplify that behaviors such as product checks with apps were too easy to conduct and resulted in less willingness to carry them out. The results suggest that it is advisable to use more challenging task when conducting self-commitments. Future studies could concentrate solely on high impact behaviors such as car-free mobility, vegan nutrition, and zero-waste shopping. An offer of fewer behaviors would possibly increase the number of participants per activity. However, a comparison of different sustainable behaviors under commitment conditions should still be possible, since little is known about the efficacy of different behavioral commitments. The example of plogging also shows that some activities might be more suitable for a collective than an individual commitment. This can help to reduce the feeling of struggling alone and, through the company of like-minded people, strengthens the feeling of doing the right thing [66,67]. Almost 80 percent of participants sustained their behavior after the commitment week had ended and, in some cases, had also tried out other sustainable actions. As participants had also recommended their behavior to others, they might have functioned as multipliers for sustainable actions.

What are practical applications? Taking into account the pros and cons, we conclude that a completely voluntary self-commitment can be a valuable approach for conservation organizations such as ‘Friends of the Earth’ to engage interested citizens in more sustainable behaviors. To the best of our knowledge, studies on the role of organizational programs for citizens’ adoption of sustainable behaviors are scarce. In the present study, we had deliberately involved the ‘District Future—Urban Lab’ in the city of Karlsruhe to distribute the invitation to our project. ‘Future Labs’ and similar transformative initiatives, overview in [72], are logical loci for action as they are the operational units in which concrete sustainability actions can be envisaged, designed, (politically) facilitated and effectively rolled out [73]. Whenever cities engage in the task of change for integrated sustainability, they also want to engage citizens in more sustainable behaviors. As already discussed as a limitation, they might first of all reach individuals with an already high personal norm to make changes. However, in the course of a self-commitment, other people can also be motivated to behave in an environmentally friendly manner, as in [18]. Apart from conservation organizations and future labs, workers in organizations could also be engaged in sustainable behaviors at work, as this is the place where they spend much of their time. One study has already shown that a self-commitment can be successful in this regard [33]. Finally, instead of lecturing on the benefits of sustainable behaviors, self-commitments would be a suitable approach to foster actual behavior in schools or universities. Some examples already exist in which students are asked to confirm on their school’s or university’s homepage what they want to take on (https://askhrgreen.org/gtk-gtd/green-classroom-take-pledge/; https://www.sustainablewellesley.com/green-cerify-your-elementary-classroom.html; https://sustainability.uw.edu/pledge, accessed on 20 June 2023).

What contributions could voluntary self-commitments make to a sustainable society? First of all, self-commitments can motivate and support individuals in carrying out a sustainable behavior that they may have been planning for some time, and in maintaining it in the long term. Secondly, they can help to motivate other people to carry out a sustainable behavior. Third, they might lead to a desire to engage in other, even more difficult to perform behaviors (spillover effect). As households are responsible for 72 percent of global greenhouse gas emissions in high-income countries, with car and plane mobility, meat and dairy consumption, and heating the most dominant components of household footprints [42,43], changes in individual consumption or mobility patterns are a valuable contribution to a more sustainable society. In this sense, self-commitments can function as a nucleus of change, especially when they include high-impact behaviors such as car-free mobility or vegan nutrition. However, as seen in the present study, structural conditions such as the number of plastic wrappings might impede pro-environmental behaviors, which makes a regulatory framework supporting behavioral changes indispensable. Policies that ban plastic packaging, for example, as well as taxation, which forces consumers to reconsider their spending and consumption behavior are needed. More efficient production systems and negative emission technologies are also important measures to achieve a sustainable future [42]. However, although individual behavioral changes alone are not sufficient to combat climate change and other environmental issues, they can make a valuable contribution to more sustainability.