Chess is a game that has evolved over centuries to pose a tough but not utterly discouraging challenge to humans, with regard to specifically human strengths and weaknesses. One human capacity it challenges is the ability to concentrate; another is memory; a third is what chess players call sitzfleisch—the ability to resist the fatigue of sitting still for hours. The computer knows nothing of any of these. Finally, chess prowess depends on players’ ability to recognize general situations that are in some sense “like” ones they’ve seen before, either over the board or in books.