The Winter War was not a colossal blunder, the Soviet Union got the territory it needed to protect Leningrad from attack, which happened a year after the Winter

The Winter War was not a colossal blunder, the Soviet Union got the territory it needed to protect Leningrad from attack, which happened a year after the Winter War ended. Also various reforms happened after the Winter War that readied the Red Army for the soon coming invasion of the USSR. There were military, and possibly political, blunders by the Soviet Union in the beginning of the Winter War, but the result was a successful one for them.