The Law of Thirds works because it's just as hard for a good team to win more than two thirds of their games as it is for a bad team to lose two thirds. That last third is tough. It may have to do with the ratio of pi to the size of an average dessert plate. You can get about a third of a pie on the plate, but that still leaves two thirds of the pie, and if you try to eat more than two thirds of a pie, it's hard. Don't even try it with a cheesecake...