Looking at the Soviet instance more closely, they were sent with a nuclear weapon into conditions where they had no communication with the outside world, and almost no information about the conditions above them or the status of the conflict, with orders to use a nuke if certain conditions were met, knowing they were being relied upon to do so. Putting aside the fact that having this kind of scenario repeated today is already very unlikely, this seems like a scenario where the use of a nuke would the least implausible. As the conditions were met, and the nuke was not used (in a scenario where it would be much more plausible than any one I’ve heard put forward today), this casts significant doubt on any speculation that military personnel would be prepared to launch nukes if ordered to do so.