“You can grade your performance in a race the same way you would grade a test in school. If you cross the finish line in the lead group, then you earned an A: you might not have won, but you never got left behind. If you are in the second group, you get a B—not great, but far from terrible; you only got left behind once. If you’re in the third group, you get a C, and so on. Each race is really a bunch of smaller races, contests that always have one of two results: you either keep up, or you don’t.”