But, if either side can obliterate the other, what does it matter who strikes first? The answer, of course, is that we are not particularly concerned with outliving the Russians by a day; we are worried about whether a surprise attack might have such prospects of destroying the power to retaliate as to be undeterred itself by the threat of retaliation. It is not our existing capacity to destroy Russia that deters a Russian attack against us, but our capacity to retaliate after being attacked ourselves. We must assume that a Russian first-strike, if it came, would be aimed at the very power that we rely upon for retaliation.

DEFINE: Distinguishes simple first-strike capacity from credible second-strike deterrence, the core logic of mutual assured destruction.

Thomas C. Schelling, The Strategy of Conflict, loc. 528