We have learned that a threat has to be credible to be efficacious, and that its credibility may depend on the costs and risks associated with fulfillment for the party making the threat. We have developed the idea of making a threat credible by getting ourselves committed to its fulfillment, through the stretching of a “trip wire” across the enemy’s path of advance, or by making fulfillment a matter of national honor and prestige—as in the case, say, of the Formosa Resolution.

Thomas C. Schelling, The Strategy of Conflict, loc. 23