When I was a child, my father taught me a trick about how to make yourself wake up at a certain time if you didn’t have an alarm clock handy or even how to remember something you had to do the next morning when you went to bed. He said that what you should do was to picture a blank blackboard, like the kind I knew from school, and then picture yourself picking up a piece of chalk and writing on the blackboard exactly what you wanted to remember the next day. “Try it and see,” he’d said to me,...