I've listened to a lot of debate about M.A.D. and whether or not it could happen. The general idea with mutual assured destruction is that nuking is never a viable tactic, because your enemy will respond with their own nukes. Not only are you destroying each other, but the rest of the planet and civilization along with it. There is no winning in nuclear war. Only losers. When that button is pushed, the answer is death. There's no questioning how fast the enemy will respond, calculations on damage, or where does you government/military go from there. The answer is death. And all of this is the biggest safeguard against nuclear war.
However some object to this idea, because they believe we are underestimating the depths of narcissism from insane dictators. Annie Jacobson describes that it only takes one insane dictator surrounded by a bunch of Yes Men, to kill the world. It's easy for us to comprehend the horrific and longterm damages of nuclear war, why it'd be a bad thing, and why there's no winning in that scenario. But we're not thinking on the same wavelength as a narcissistic, egotistical dictator. Perhaps one who's getting older and more disillusioned. Granted there's no a big red button in every world leader's bedroom that says "Nuke" on it, and they're the ones who decide AND push the button. There's usually an order that gets passed down a chain of command. But if that happens, you can't bet on having another Stanislav Petrov save us from annihilation. We were incredibly lucky that man was on station that day.
So I guess this is all to say never say never. It could happen, and as long as nukes continue to exist, then statistically speaking it's likely inevitable.