Earlier quoted context omitted.
And what comes after the nuclear exchange? A military conflict is 90% logistics. To rebuild, a nation that is well prepared for catastrophe will manage.
The whole idea is that potential damage is so high that it makes no sense to start conflict. MAD so far worked good enough to prevent major powers from going to war.
1) eventually, there will be a madman in charge of the nukes. Only a matter of time. As long as there are nukes, I believe they will eventually be used.
2) another option to consider. MAD assumes the 1st strike party will also be annihilated. Perhaps someone will figure out a way to use their nukes first while somehow preventing a counter strike. “Unknown unknowns“.
3) technical malfunction