This is the key point. Your friends strongly influence how you perceive reality. First, they strongly influence how you see yourself. It’s very hard to measure your own worth, your own competence, unless people you admire and respect see you as worthy, see you as competent. Plus, if your friends say, “We’re all smart, talented people,” you’ll begin to see yourself that way, too.
Second, your friends shape how you see the world. A few decades ago, a theorist named James J. Gibson pioneered the theory of “affordances.” The basic idea is that what you see in a situation is shaped by what you are capable of doing in a situation. Dennis Proffitt of the University of Virginia has demonstrated this theory in a bunch of ways: People who are less physically fit perceive hills to be steeper than people who are fit, because they find it harder to walk up them. People carrying heavy backpacks perceive steeper hills than people without them.
The phenomenon works socioeconomically, too. Kids who grew up with college-educated parents walk onto the Princeton campus and see a different campus than kids who have never been around a college at all. Without even thinking about it, more-affluent kids might communicate to their less-affluent friends ways of seeing that make such places look less alien, less imposing, more accessible.
Third, our friends alter our desires. Desire is notoriously mimetic. We want what other people want and tell us is worth wanting. If you grow up around friends who naturally aspire to be doctors and accountants and engineers, you are probably going to aspire to such things, too.
Entering into a friendship can be a life-altering act, and entering into a friendship with someone different from yourself can be life-transforming. The philosopher Alexander Nehamas argues that when we enter into a friendship, we’re surrendering our future selves to that relationship, in part because the friend may call forth parts of ourselves that don’t yet exist.
Writing in Comment magazine, David Henreckson observes that when you venture into a new friendship you may wind up taking on new interests, new pursuits and even new enemies. It’s daunting: “If in the early days of a relationship we knew all the ways that a particularly intimate friendship would change us, how it might transfigure some of our core values, we would be excused for being a little bit reluctant to jump in.”