The cost-benefit analysis of a strategic nuclear strike is: cost=everything, benefit=revenge? It's a horrible decision that nobody would make. But the cost-benefit analysis of Russia using a hypersonic IRBM to attack a Ukrainian military target is: cost=(a missile, probably provoking a further escalation that will undoubtedly be calculated to cost more than the benefit), benefit=(maybe it will cause the other side to think twice instead of escalate, destroys an enemy missile factory). Still the wrong decision to escalate, but it is not as dumb as the nuclear strike.