Author's Note: Last week, my colleague wrote why he was wrong about Ukraine . This week, it's my turn. I was also wrong about Ukraine. I thought the Russians would formalize their de facto control of the separatist republics in eastern Ukraine's Donbas region and perhaps grab a bit more territory in the surrounding areas (and near the Crimean Peninsula, which they had already annexed). But I did not think Russia would launch a full-scale invasion. In retrospect, there were many reasons for my analytic failure — not least of which was underestimating Russian President Vladimir Putin's risk tolerance. But one key indicator I undervalued was Putin's focus on the supposed need to ''denazify'' Ukraine in advance of the invasion. Had I given more weight to that variable, I may have forecast differently.