Hmm, TechRep, I'm not sure I agree with you about Dunkirk, purely because had Germany pushed on and wiped out most of the British forces it would have cost about 200,000 troops (some would have got away), but Germany would still have been unable to invade Britain because the RAF would still have stopped them. However, the political climate might have been such that Britain would have sued for peace. Certainly being able to portray the event as a victory rather than a defeat (though defeat it was, just not as bad as it could have been) steeled the British resolve and made them determined to fight on at all costs. However, in the Battle of Britain, the decision to switch from attacks on airfields and radar to attacks on the cities was a major blunder. In all of these situations it is easy to see where the Germans went wrong, but very hard to pin down one event as being decisive.
You may disagree with that analysis, it is, after all impossible to prove. But worth thinking about, nevertheless.
As for the invasion of Russia, what made that even worse was that Napoleon had done exactly the same thing over a hundred years before, with the same outcome. With the benefit of hindsight it can be said that Germany was almost certain to lose that campaign anyway sooner or later, unless, again, the political situation came into play.
I don't agree that Pearl Harbor was a mistake. Japan intended to be the pre-eminent power in the Pacific, and would have come into collision with the US sooner or later. That being a given, the attack on Pearl Harbor was militarily sound, and gave them their only chance of success. The fact that it was ultimately unsuccessful doesn't change that.
She's as nervous as a very small nun at a penguin shoot.