But it is not clear just where the line can be drawn in advance. “Hostility,” for example, might seem to be an emotional or temperamental quality best kept out of game theory; but if a player’s hostility in the game is a significant constraint on his ability to perceive the other player’s meaning, it becomes part of the “communication structure.” An experiment by Deutsch is pertinent. He let pairs of players play nonzero-sum games (in matrix form) tacitly for a sequence of two plays, the game providing both a “cooperative” and an “uncooperative” choice. Those who played uncooperatively against a cooperative partner had an opportunity, on the second play, to respond to the implicit offer of cooperation. But, “when their expectation of the other person’s choice was not confirmed, they tended to interpret his choice as being a function of indifference or a basic lack of understanding as to how the game ‘should’ be played. . . . In this group, knowledge of the other person’s choice, because of the meaning attributed to it, tended to reinforce the previous negative sentiments regarding the intentions of the other person.”

Thomas C. Schelling, The Strategy of Conflict, loc. 795