The first point to observe is that a commitment, a promise, or a threat can usually be characterized in a fashion equivalent to the following: to make one of these moves, a player selectively reduces—visibly and irreversibly—some of his own payoffs in the matrix. This is what the move amounts to. {81} We could also say that one openly selects a strategy in advance for responding to the other’s choice; but more than selection is required. The player must invoke penalty on his own failure to pursue subsequently the particular strategy of response that he has selected beforehand. And to invoke a penalty on failure to follow a strategy is mathematically equivalent to subtracting the amount of the penalty from one’s own payoffs in all cells that do not correspond to the strategy so selected.

Thomas C. Schelling, The Strategy of Conflict, loc. 347