Once you start questioning the reality of memory, things fall apart pretty quickly. So many of our assumptions about the human mind—what it is, why it breaks, and how it can be healed—are rooted in a mistaken belief about how experience is stored in the brain. (According to a recent survey, 63 percent of Americans believe that human memory “works like a video camera, accurately recording the events we see and hear so that we can review and inspect them later.”) We want the past to persist, because the past gives us permanence. It tells us who we are and where we belong. But what if your most cherished recollections are also the most ephemeral thing in your head?