From this follows the significant feature. The last offer that it is mechanically and legally possible for a player to make is one that he necessarily makes without knowing what the other player's final offer is going to be; and the last offer that a player can make is one that the other player cannot possibly respond to in the course of the game. Prior to that penultimate moment, no offer has any finality; and at that last moment players either change or do not change their current offers, and whatever they do is done in complete ignorance of what each other is doing, and is final.

Thomas C. Schelling, The Strategy of Conflict, loc. 617