Isn't the lesson here that the west has a very different attitude to risk than Russia. We have shown ourselves unwilling to risk Russian retaliation and western loss of life and infrastructure.
I think that's part of it, but surely only a small part. We are massively more powerful than the Russians, and MAD prevents the outbreak of nuclear war, so that's not even in the equation (there are too many human blobs of jelly in this thread who never lived through the Cold War, and it shows.)
I think the biggest issue is that the West considers open war with Russia to be politically toxic for domestic voters, because we'd have to actively attack a country that hasn't attacked us.
So Ukraine will be sacrificed via the death of a thousnd cuts because our politicians aren't prepared to stop thiknking about next week's poll and start thinking ahead to the shape of Europe in the next 30 years.
Sometimes upopular decisions must be made. Move NATO forces into Ukraine and dare Russia to attack them. Then keep moving them right up to the border of Crimea.
Then roll into Crimea and let the war machine do what it does best.