what a game of chess would be
George Eliot in her novel Felix Holt wrote
"Fancy what a game of chess would be if all the chessman had passions and intellects, more or less small and cunning; if you were not only uncertain about your adversary's men, but a little uncertain also about your own . . . You would be especially likely to be beaten if you depneded arrogantly on your mathemactical imagination, and regarded your passionate pieces with contempt. Yet this imaginary chess is easy compared with a game man has to play against his fellow-men with other fellow-men for instruments."
Dealing with other 'fellow-men' isn't a calculation like accounting is a calculation. It's a much more complex activity, a calculation on how likely another person will, in Axelrod's terms, defect or co-operate. And the calculation is made on imperfect knowledge, on reputation, on words and on faces. Our interpretation of these triggers our response.