M.A.D. is a doctrine of military strategy in which a full-scale use of nuclear weapons by two or more opposing sides would cause the complete annihilation of both the attacker and the defender.
It is based on the theory of deterrence, which holds that the threat of using strong weapons against the enemy prevents the enemy's use of those same weapons.
In the context of the Cold War, the only "stable" state was for both sides to have enough weapons to destroy the other, even after absorbing a first strike. This paradoxical logic kept the peace for 50 years.
Input
If I strike, I die. If I don't strike, I live (probably).
Output
Do not strike. Build more bombs to ensure I can strike back.