From “Lore of Running”, Chapter 10 by Tim Noakes, MD

The marathon is less physical event than a spiritual encounter. In infinite wisdom, God built into us a 32-km [20 mile] racing limit, a limit imposed by inadequate sources of the marathoner’s prime racing fuel – carbohydrates. But we, in our human wisdom, decreed that the standard marathon be raced over 42-km. So it is in that physical no-man’s land, which begins after the 32 km mark, that the irresistible appeal of the marathon lies. It is at that stage, as the limits to human running endurance are approached, that the marathon ceases to be a physical event. It is there that you, the runner, discover the basis for the ancient proverb: “When you have gone so far that you cannot manage one more step, then you have gone just half the distance that you are capable of.” It is there that you learn something about yourself and your view of life.