People with borderline personality disorder and certain other conditions, such as autism, have trouble comprehending social norms. People with borderline, or BPD, as it’s abbreviated, struggle with mentalizing, or guessing what other people are thinking. They tend to be hypermentalizers—they interpret people’s intentions in the worst way possible, and they don’t react, well, normally. People with BPD sometimes come from difficult homes, or they have unusually sensitive temperaments.

“Your first laboratory to learn how to read the minds of other people is your family environment,” explained Carla Sharp, a professor at the University of Houston who has studied the disorder. It’s where you learn “that it’s okay to ask someone what you’re thinking, that it’s okay to change your mind.” For some people with BPD, this laboratory failed. They didn’t get to practice “the literacy of interaction,” as she puts it. Social norms are the first book we all learn to read.

Norms, though, are fickle friends. On the positive side, the tipping norm pays waiters’ salary and the “don’t walk into traffic” norm prevents chaos and carnage in the streets. Most people like following norms, and they like people who do, because we don’t like to be surprised by every single thing that happens. The rhythms of small talk and office speak steady us with their predictability.

In her masterful study of social norms, The Age of Innocence, Edith Wharton22 describes a “hieroglyphic world” of Gilded-Age New York. At first, the couple at the center of the story—Newland Archer and his fiancée, May—happily follow these rigid formulas. “Nothing about his betrothed pleased him more than her resolute determination to carry to its utmost limit that ritual of ignoring the ‘unpleasant’ in which they had both been brought up,” Wharton writes of Archer early in the book.

But later, Archer leaps to the defense of May’s cousin, Ellen Olenska, saying her “unhappy life”—a scandalous and very norm-violating separation from her husband—“doesn’t make her an outcast,” despite what those around him claim.

As Archer found, norms can also hold us back. They give us structure, but they punish anyone who dares break free of them. “Norms are inherently conservative,” says Chris Crandall, a psychology professor at the University of Kansas. “We tend to persist in doing what the people before us did.”

Countless interracial couples suffered, for example, when there were strong norms against so-called miscegenation. In maintaining social order, norms can make things too tidy. Norms freeze our lives in amber, a process that can be beautiful, but also deadening. To return to our fictional example, because of the norm that one should marry “well” and stick with one’s partner, Newland Archer is never able to be with Ellen, even though he realizes he loves her more than May.