After this week’s devastating military setbacks for the Ukrainian government, Western observers are trying urgently to get inside the head of Vladimir Putin. But the practitioners of this burgeoning cottage industry—call it Putinology—are missing one essential point: Mr. Putin has largely been improvising his way through the current crisis. That means that the Ukraine showdown is even scarier and more dangerous than you think: Mr. Putin is making it up as he goes along.

The Russian leader has routinely experimented with (and...