I don't think invading Russia was a bad decision per se, the problem is invading Russia during the winter which is what should have been learnt from Napoleon, who's army was destroyed by the winter, not by the Russian army. There was a long distance to cover to Moscow, and Germany should have attacked around the start of spring, not 22 June (Napoleon attacked on 24 June). If that was not possible during 1941, they should have waited till 1942.

More irrational was Hitler's decision to order troops at Stalingrad not to retreat, saying roughly "Too many German lives have been lost to retreat now" which is very much sunk cost bias. For that matter, the decision to prioritise Stalingrad was made because of the name. True, capturing the city named after the Russian leader would have damaged morale, but this is a political argument, which Hitler may have overestimated because his expertise was in politics. Perhaps actually trying to capture the oil fields, while more mundane, would have been a better objective?

Towards the end of the war, Britain had a plan to assassinate Hitler, but chose not to put it into action partially because Hitler was acting irrationally and whoever succeeded him would perhaps have been a better military leader.

+1 for a novel/interesting original post.

I agree the idea that evil/irrationality go hand-in-hand is a commonly held, but silly idea. In a similar vein I see people thinking the line between good/evil is distinct and clear-cut throughout history. If we believe it was a clear distinction historically, it should follow the distinction would be clear today. And who is evil today? Our political opponents, of course (/s).

Not to suggest there weren't better/worse sides in the past, however, I recently read this book 'Human Smoke,' which is a collection of news paper clippings from the 1920s-1940s. It's incredible how a few years before WWII Churchill was gassing and decimating colonialist towns for disobeying imperial mandate. It is only one data point, of many, to show that this idea that good = rational, morally upstanding, our side. Bad = evil, irrational, crazy, their side. Is a vast oversimplification.

PS: Your post also reminds me of War and Peace, where Tolstoy makes the argument that attributing Russia's defeat of Napoléon as due to some grand strategic brilliance is nonsensical, and the reality was more mundane (One example, a combination of bureaucratic slowness leading to retreat, luckily paired with a colder than usual winter).

Another aspect to consider is that Hitler had spent the decades leading up to the war declaring the Soviet Union to be an existential threat and noisily pre-committed to a massive seizure of Eastern European land. He dedicated an entire chapter to the topic in Mein Kampf. So Hitler had perhaps already tied his own hands before he even came to power.

The decision you're talking about was indeed fatal, but "most fatal?" Hitler tried to kill all of Albert Einstein's people, with the result that Einstein wrote a letter to the President explaining the idea of nuclear weapons.

the Germans were not crazy to think that they would eventually have to fight the Russians.

In my model they absolutely were, because evil and stupidity do not always go together. Stalin was a rational psychopath who kept every promise he made to a foreign power. (If he believed or cared about Communist ideology at all, he thought it rendered war against another major power redundant and foolish.) He thought Hitler was the same, to the point of not listening to anyone who said otherwise, and finding the truth shocked him into paranoia.