Hippocrates, the Greek physician and namesake of the “oath,” believed that people’s personalities were governed by the amounts of phlegm, blood, black bile, and yellow bile that flowed through their bodies. Depending on the levels of these fluids, people could be classified as melancholic, or anxious introverts; phlegmatic, or relaxed introverts; sanguine, or relaxed extroverts; and choleric, or anxious extroverts.309 Notions of bile and humors, of course, have long since been discarded by modern science. And now, as the psychologist Richard Wiseman put it in his book The As If Principle, it appears the idea that our personalities are immutably biologically programmed is also not quite true. The book’s title comes from the idea that you can behave “as if” you are the person you want to be. Pretty soon, you might find that it is you. This means that if you’re an introvert—or disorganized, or not punctual, or quick to judgment—you don’t have to stay that way forever.

Of course, not all people who are different should or can change their personalities. They should not have to contend with discrimination, no matter what their disposition is like. But while we work at ending prejudice, we can also be living the lives that we want. In some cases, like Curt’s, a personality change can be helpful, especially when the change leads to more friendships and social connections, rather than further isolation.

Few people are as ready and willing to transform their entire personalities as Curt was. But research suggests that personalities are fairly flexible, and for those who are interested in changing themselves, change is not only possible, it can happen rather quickly.

Many researchers have now found that adults can change the five traits that make up personality: extroversion, openness to experience, emotional stability, agreeableness, and conscientiousness. Changing a trait primarily requires acting in ways that embody that trait, just as Curt did, rather than simply thinking about it. For example, in one study,310 putting more effort into homework led students to become more conscientious—a reversal of the popular idea that conscientious students put more effort into their homework.

A personality change can occur across a variety of other domains and ages. Gigi Vorgan, coauthor of the book Snap!: Change Your Personality in 30 Days, gives the example of an elderly couple in which the wife, Audrey, wants to move across the country, but the husband, Howard, isn’t sure about the idea. Howard could start using strategies to slowly increase his level of “openness,” such as going to a new restaurant. “Ideally, with time, these improved behaviors and thinking patterns will transition into new habits,” Vorgan told the Wall Street Journal.311