The Russian government must be well aware of the consequences that would be likely to follow: immediate and comprehensive economic sanctions by the West, an expansion of the Magnitsky List with asset freezes and visa bans on Russian officials, an embargo of Russian companies and banks, exclusion of Russia from the G8 and other international bodies, and a great deal more. It seems improbable, therefore, that Putin is really willing to risk finally destroying Russia's already fragile and ailing economy and society by taking such a step - if, that is, he is a rational actor.
The explanation advanced by observers like chess master and human rights activist Garry Kasparov is that in the international and domestic public sphere alike, the rationality of Russia's leaders only extends so far - at a certain point it veers off into demagogic muscle-flexing and posturing:
Putin doesn't need to "win" in Crimea / Ukraine. Only to show power, look tough. This is what dictators do instead of having real elections.
— Garry Kasparov (@Kasparov63) March 2, 2014