These two parameters, Pc and Pr, are assumed to be plainly visible to the two players; there is nothing secret or conjectural about them. This assumption might seem to beg the question we are trying to answer, but it does not. These two exogenous likelihoods of attack do not by themselves indicate what the probability is that the players will in fact attack. They are only one element. The problem is to see whether, given these basic sources of uncertainty, the interaction of the two players’ expectations generate additional motive to attack.

DEFINE: Distinguishes exogenous likelihood parameters from the endogenous probability of attack that emerges from interactive expectations.

Thomas C. Schelling, The Strategy of Conflict, loc. 470