If we are to avoid adding a whole new dimension to our payoff matrix, in the form of discount rates, we must suppose that the game is terminated soon enough so that nothing like the interest rate enters the picture. We do not want to have to consider the time at which agreement is reached, in addition to the agreement itself. This is more than a matter of convenience; the game ceases to be "moveless," except in very special cases, unless we make this stipulation. For, if the players' time preferences take any shape except that of a continuously uniform discount rate, the game itself changes with the passage of time and a player can, in effect, change the game itself by failing to reach agreement.

Thomas C. Schelling, The Strategy of Conflict, loc. 613