“how do you get those particular clusters of neurons to fire at the right time? One way is to go for a walk. The history of innovation is replete with stories of good ideas that occurred to people while they were out on a stroll. (A similar phenomenon occurs with long showers or soaks in a tub; in fact, the original “eureka” moment—Archimedes hitting upon a way of measuring the volume of irregular shapes—occurred in a bathtub.) The shower or stroll removes you from the task-based focus of modern life—paying bills, answering e-mail, helping kids with homework—and deposits you in a more associative state. Given enough time, your mind will often stumble across some old connection that it had long overlooked, and you experience that delightful feeling of private serendipity: Why didn’t I think of that before?”