We often think that self-control comes from within, yet many of our actions depend just as much on our friends and family as ourselves. Those we surround ourselves with have the power to make us fatter, drink more alcohol, care less about the environment and be more risky with sun protection, among many things.

This is not simply peer pressure, in which you deliberately act in a certain way to fit in with the group. Instead, it is largely unconscious. Beneath your awareness, your brain is constantly picking up on cues from the people around you to inform your behaviour. And the consequences can be serious.

It is now well accepted that our personal sense of self is derived from other people. “The more of your identity you draw from a group, even when you’re not around that group, the more likely you are to uphold those values,” says Amber Gaffney, a social psychologist from Humboldt State University. “If a big part of how you identify is as a student from a certain university, or like me an academic, then that’s what you take with you into most interactions with others. I see things first through my lens as an academic.” Students, for instance, tend to have stronger attitudes towards things like legalising drugs or supporting environmental sustainability than the rest of the population.

These are called social norms. And while these norms are usually stable, some interesting things happen if just one person in the associated group acts out of character.

Consider the following study, which found that people were likely to change their opinion on green travel if they found out their peers were acting hypocritically.

The students from Humboldt State University reside in a small, socially liberal town in northern California which takes pride in its environmental credentials. The students there are largely very environmentally conscious, too. You would expect that a peer’s disregard for carbon emissions would not go down well.

After listening to an interview with a student at the university who stressed the importance of walking or cycling short distances rather than taking a car, and then later admitting to driving to the interview, the participants were asked about their own environmental views. They did this while sat next to an actor. The actor took the role of either a third student wearing a university sweatshirt, or a professional in smart clothing. When the hypocrisy of the interviewee was revealed, the actor either made a negative remark about their behaviour or stayed quiet.

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How the participants judged the importance of walking or cycling short distances was dependent on who they listened to the interview with, and how that person reacted. When sat with someone they thought was another student, and who shared their environmental values, the participants reiterated the importance of cycling. When sat with an outsider it wasn’t so clear cut.  

An outsider who commented on the hypocrisy of the interviewee elicited the strongest environmental feelings in the participants. By defending the interviewee from criticism, they reinforced their own view that cycling was important. This is perhaps because they felt the interviewee might normally be more environmentally responsible. Conversely, if the outsider stayed quiet, the participants judged the importance of cycling the lowest. So, how an outsider judges our peers has a big impact on whether we back them up or not.

“This was an interesting study,” adds Gaffney, “because we were able to make some people care less about the environment. Normally this isn’t something that we would actively want to do, but understanding where these views come from could help us to nudge people in the other direction.”

In the face of criticism by a stranger, we might come to the aid of our peers. But if left to form our own opinions, we interpret the hypocritical behaviour as a sign that we can relax our own views. This is called vicarious dissonance.

“Vicarious dissonance is when you see someone behave in a way inconsistent with your attitudes, so you change your attitudes,” says Gaffney. “I should be embarrassed by seeing you act in a non-environmental way, but that doesn’t always happen. I won’t necessarily start copying you, but I will change my attitudes to reflect your behaviour because I feel similar to you and I see you as an extension of myself.”

This study was inspired by several pieces of work in Australia on vicarious dissonance around sun protection use. Again, someone acting hypocritically would relax people’s attitudes around applying protection, where the norm is to be extremely vigilant.

How we talk about our health choices with friends can also have a significant impact on our decisions, both positively and negatively. Talking about an anti-smoking campaign with friends reduced people’s cigarette intake, perhaps because those conversations gave smokers the opportunity to work out which information was most relevant to their lifestyles – and then act on it. This is supported by a meta-analysis of 28 studies totalling 139,000 participants.

“The leading cause of death is preventable health behaviours like smoking and obesity, and we have access to a vast amount of information online but we still smoke and we still don’t exercise,” says Christin Scholz of the University of Amsterdam. “Anything our friends do influences us in ways that we are conscious of or not. Their presence can decide whether we act on that health information or ignore it.”

Scholz asked college students in the US if they had talked to anyone about a recent experience involving alcohol, and whether those conversations were positive or negative. If they had talked positively about alcohol consumption they were more likely to drink more the next day, and vice versa. These patterns are highly influenced, though, by the social circumstances that we find ourselves in.

When we make decisions we are constantly reassessing the value we might get from each choice – a process called value maximisation. Our decision to take the stairs rather than a lift is dependent on how much we ate at lunch, if we have already been for our daily run and whether we walked into the building with our triathlete colleague. No effect of a conversation with friends can ever be viewed in isolation. And that is why our willpower fluctuates.

“Say I have a conversation with a friend the day before about some of the negative sides of alcohol but the next day I am in a bar with other people – I would still argue that conversation has some form of influence on me,” says Scholz. “However, it’s a pretty simple representation of human decision making. We’re not always [very] rational – we make these decisions pretty quickly. The importance of certain types of information changes through the day.”

Our choices are influenced by who we are with when we are asked the question, how those people reacted, any conversations we might have had beforehand and our fundamental understanding of what is normal for that group of friends. But, if we’re still in doubt, the easiest thing to do is to look at what others are doing and copy them. We do this all the time, and we might not realise the impact it has.

When we eat with people who eat a lot, we eat more

“When we eat with others we have a natural tendency to use their behaviour as a guide,” says Suzanne Higgs, who studies the psychobiology of appetite at the University of Birmingham. “Lots of studies have shown that when we eat with people who eat a lot, we eat more. People aren’t often aware they are being influenced in that way. They might say it was the taste or the price or hunger levels rather than the people around them.”


The phenomenon was first described based on an analysis of food diaries by John de Castro in the 1980s. These detailed diaries listed what people ate, but also where, when and who with. He was then able to control for the effects of celebratory meals, whether alcohol was consumed, if the meal took place at the weekend and any other factors that might have influenced the amount of food eaten.

These effects have since been repeated in laboratories. Higgs asked students to eat lunch either with a friend or in isolation in a lab. It appears to happen even when you are eating with one other friend in a very controlled environment. But, this effect only occurs with people that you know well.

The presence of another person clouds our ability to pick up on cues from our bodies that we are satisfied

Higgs suggests that the presence of another person clouds our ability to pick up on cues from our bodies that we are satisfied. The normal process of feeling full is disrupted by feeling stimulated by our friends. Other distractions, like watching TV, have been shown to increase food consumption.

Next, Higgs took her research into the field to see if eating behaviours could be influenced by other social cues. She wanted to encourage people to choose vegetable side dishes by providing information about the choices of other diners using posters. “Of course we know that explicitly saying ‘Vegetables are good for you’ doesn’t work,” says Higgs. Instead, the posters displayed fabricated data about which side dishes most customers bought. Higgs put a vegetable side dish at the top.

“These posters just described the behaviour of other people – and that’s enough for some,” says Higgs. “When we enter a new environment, we look for cues about how to behave. So, to see that a certain choice is the most popular really helps us out.”

The effect was seen even after the posters were taken down. Higgs had created a new norm.

“There is good reason to believe that when we use normative behaviour it makes us feel good because we’re connecting with a social group,” says Higgs. “If you are with a new social group, you are more likely to imitate behaviours.”

Our decisions might not always be in our hands. But this also means we can use our influence for good. “The same way a negative behaviour can spread through a network of people a positive one can spread through a network,” says Scholz. “We’ve evolved to live in a group to spread positive actions and to seek the approval of others.”


William Park is @williamhpark on Twitter.

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