I was with you about 3/4s of the way. I don't think Russia invaded because they knew they would win. I think they invaded because they knew waiting would assure that they would lose.

Particularly Putin*s own statements and activities in the early days of the sanctions and the invasion, and actions on the ground support since then support my theory.

Putin felt that the Soviet Union made a huge error with the Nazis. 1 in 7 Russians were killed in WWII, and the biggest force came through Ukraine. Putin has said Russia waited far too long in WWII, and the country suffered massively. He didn't want to repeat that error.

That does NOT mean that Russia knew they would win. Until it became clear that India would buy more oil, and China would buy more oil and gas, it looked like the sanctions might work. The Russians (IMO) thought Ukrainian resistance would be much lower.

I think they just didn't see a way out without invasion. Maybe there was one, but after looking for 18 months I've not heard a plausible one.