Imagine a footrace. A hundred runners assemble at the starting line, but when the starter's pistol goes off, ten of them change their minds and don't run at all. At the first turn, another dozen drop out: They're too far behind, and they feel like they can never catch up. Halfway into the race, still more quit: They're tired, they're sore, and they don't think they can make it. With the finish line in sight, still more grind to a halt: They haven't paced themselves, and they can't go on. By the time the runners reach the finish line, only a handful are left.