The feeling of having no choice tends to be influenced by incentives, though. Had NATO mobilized 5 million soldiers in eastern Poland in late 2021, with the clear message that they would send those forces into Ukraine if Putin attacked, he would probably feel differently.

Personally, I think he may have felt "it's now or never". It appears he started preparing directly after the 2020 election, and he may have misjudged Biden, thinking him too weak to respond.