When did you last immerse yourself in the pool of make-believe? In a television drama, or a film, watched from the sofa or a cinema seat? A story you just read to your children? The comic strip you read in this morning’s newspaper? A joke you heard at work or around the table? The novel you read last night? A love song on your iPod? Chances are that the last fictional story you encountered was not long ago, and the previous one not long before that.

Why do we spend so much of our time in story worlds, from pretend play and fairy tales to novels, comics, TV sitcoms and vampire series, movies from Hollywood to Bollywood and arthouse, and the stories in poems, song lyrics and computer games? Wouldn’t you expect a successful species, as we seem to be, to spend its time focusing on what’s true in the world? But we, uniquely, often distract ourselves with what we know to be untrue.

I teach literature, and fictions beat at the heart of literature. I don&rs...