Frank Shorter

It is only when you watch the dense mass of thousands of ants, crowded together around the Hill, blackening the ground, that you begin to see the whole beast, and now you observe it thinking, planning, calculating. It is an intelligence, a kind of live computer, with crawling bits for its wits.

Train at the same pace day after day, week after week, year after year, and that's the kind of running the body adapts to. But break out of that comfort zone with a little speedwork now and then, and the body will learn to deal with the new demands.