Brian Little, one of the world’s leading experts on personality psychology, is renowned as a public speaker. If you watch his recent TED talk on personality, as millions of others have, you will see an engaging and witty orator holding his audience’s attention with aplomb. You’d probably conclude that Little is an extravert: he’s not only good at what he’s doing, but he seems to be revelling in the opportunity.

In fact, Little is a self-proclaimed introvert. After his talk you would quite likely find him seeking a few minutes of quiet refuge behind the locked door of a toilet cubicle. This is one of the “restorative niches” described in his 2014 book Me, Myself, and Us, which he uses to recover from the exhausting demands of acting extraverted.

Little can behave extraverted when he needs to, he explains, because he is enacting what he calls a “free trait”: behaving out of character in pursuit of a deeply meaningful “personal project”, which in this case is to engage and educate his students and others in the value of personality psychology. This isn’t a peculiar quirk of this Cambridge University professor. He believes that each one of us is able to act out of character when we are motivated by an important and meaningful personal goal.

Indeed, Little and his colleagues have spent many years studying how we can break free from the constraints of our more permanent personality traits, and live a happier life too.