Third, during mind-wandering, your mind will—Nathan said—engage in “mental time-travel,” where it roams over the past and tries to predict the future. Freed from the pressures of thinking narrowly about what’s right in front of you, your mind will start to think about what might come next—and so it will help to prepare you for it.

So we sit and focus our attention on our breathing. But before long, the challenge becomes obvious. The human mind is an unpredictable and wildly creative creature that seems to have a life of its own. It produces an astonishing array of content, images, phrases, memories, emotions, and insights. Sometimes that content is inspiring and intelligent,