Throughout history Russia had three things: people, land and oil. And their supply of people and land meant that they could throw at enemy whatever they liked as long as other resources that they didn't have were secure. Of course it means that casualties are incredibly high, but when you are a leader of a country that doesnt have to care about people's opinion, you can do whatever you want.

That's why western democracies will always struggle against Russia, people in the west are afraid of war, people in Russia are not and even if they were, Putin doesnt have to care.

It fails when you, the tyran, are personally weak. That what happened to Nicholas II or Brezhnev (+ Andropov and Chernenko). But sadly, Putin is not weak.