The people who would actually launch the missiles would be the same people who told Putin that the Ukraine invasion would be a walk over.
They where told it wasn’t going to happen, just some postering before going back to normal. They said ‘yes, we could theoretically walk over Ukraine’ believing they wouldn’t have to follow up on that.
They know dam well there is no theoretically winning a nuclear exchange, meaning they won’t tell their superiors they can do it and no superiors that would believe them if they did.