Julia Ioffe of the New Republic explains:
“We didn’t think Putin would do this. Why, exactly? This has often puzzled me about Western analysis of Russia. It is often predicated on wholly Western logic: surely, Russia won’t invade [Georgia, Ukraine, whoever's next] because war is costly and the Russian economy isn’t doing well and surely Putin doesn’t want another hit to an already weak ruble; because Russia doesn’t need to conquer Crimea if Crimea is going to secede on its own; Russia will not want to risk the geopolitical isolation, and “what’s really in it for Russia?”—stop. Russia, or, more accurately, Putin, sees the world according to his own logic, and the logic goes like this: it is better to be feared than loved, it is better to be overly strong than to risk appearing weak, and Russia was, is, and will be an empire with an eternal appetite for expansion. And it will gather whatever spurious reasons it needs to insulate itself territorially from what it still perceives to be a large and growing NATO threat. Trying to harness Russia with our own logic just makes us miss Putin’s next steps.”
For once, TNR gets it pretty much right. Remember, nations don’t have friends, only interests.