Look at the graph below, which comes from researcher George Wu at the University of Chicago. It summarizes the completion times of more than nine million runners in marathons from Chicago to Berlin.5 You can see that most runners finished a marathon in 3.5 to 5 hours. But notice how the graph looks spiky. Pay attention to the vertical lines showing the “threshold” times: 4:00:00, 4:30:00, 5:00:00, and so forth. You’ll see that a lot more runners finished just before the lines than just after them. (It’s particularly dramatic at the 4-hour mark.)
