> Put differently, Putin does not roll a dice every morning and launches a nuclear missile if a six shows up. Even he himself cannot meaningfully answer the question “What’s the probability that Russia will launch nuclear missiles 6 months from now” unless his answer is 100%. It depends on many factors, like how NATO reacts and how strong the Ukraine military is, none of which can be captured by probabilities.

There's a guy[0] who spent a career analyzing and writing about these things.

His most recent take is that by refusing to get directly involved in Ukraine, NATO creates an understanding in Putin's mind that it wouldn't get involved in, say, Latvia either. According to Piontkovsky, (to Putin,) there's no essential difference, and the (lack of) NATO membership reason provided by NATO is a lame excuse indicative of a lack of resolve to commit, NATO member or not. So Putin is willing to keep upping the ante until NATO folds and becomes irrelevant.

[0]https://www.researchgate.net/publication/313258664_Putin's_R...