““We live in what might be called a nearly empty world-one in which there are millions of variables that in principle could affect each other but that most of the time don't. In gravitational theory everything is pulling at everything else, but some things pull harder than others, either because they're bigger or because they're closer. Perhaps there is actually a very dense network of interconnections in the world, but in most of the situations we face we can detect only a modest number of variables or considerations that dominate. If this factorability is not wholly descriptive of the world we live in today-and I will express some reservations about that-it certainly describes the world in which human rationality evolved: the world of the cavemen's ancestors, and of the cavemen themselves. In that world, very little was happening most of the time, but periodically action had to be taken to deal with hunger, or to flee danger, or to secure protection against the coming winter. Rationality could focus on dealing with one or a few problems at a time, with the expectation that when other problems arose there would be time to deal with those too.””
