Comment by bell-cot

Unfortunately and fortunately, MAD and "launch it or lose it" are far-too-simplistic descriptions of the situations facing the decision makers. Unless a side's leaders are very narrow fanatics (vs. mere posturing as such for political benefit), "winning" an all-out nuclear war via first strike is a pretty shitty victory. Whether or not you believe in nuclear winters, the world would be a huge radioactive mess, with enormous social and economic disruptions, and your regime very widely blamed (and widely hated) for that. Ambitious underlings and rivals could see your removal from power as the obvious next step. Having to stay united against the (now destroyed) Great Enemy may have been a cornerstone of your regime's political stability.

Meanwhile, the leaders on the other side are aware both of those considerations, and of the history of near-disasters resulting from false alarms of enemy nuclear attacks. Making their own launch decisions much more complex.