The mistake in WWII was probably starting the invasion of Russia in the first place, but certainly being overambitious. I would have to re-read my history but I'm fairly sure at one point there was a debate over whether to go for Moscow, or for the rich oilfields of Southern USSR and the Caucasus region. And Donbas, which is sadly the scene of the today's War... but, in any case, by not really committing to either of these fully, the Nazis ended up achieving neither.
It also turned out that the Soviet manpower was many times higher than estimated, so that despite their huge early losses, the Soviet Army ended up stronger after the invasion than it had been before. In the event, I think the German advance came within around 10 miles of Moscow, but never any further; had that been the initial objective, rather than the oilfields, then who knows how things might have turned out? It was a close-run thing.