Quite true Randall, but, in both cases, it was the fact that the majority of the German concentration was in the east, that even allowed the western allies to be there. One more division at Anzio, and it would have crushed the landing. One more division at Normandy, or even the "chief idiot" Hitler, allowing the panzer reserves that already were there, to move up sooner, and that landing would have been a disaster that the allies would not have recovered from. This was known to the allied generals, also, in the case of Eisenhower, who held a note in his pocket apologizing for the disaster, "just in case"..and the British general Brooks, who expected a disaster.
Deception efforts caused the Germans to spread so thinly trying to cover many unreal targets, so that they could not concentrate on the real one, a great job, a great strategy, but HARDLY a "sure thing"...and much less so, had not the Wehrmacht still put about 60-65% of their effort in the east. Even going beyond, since it is a game, had Hitler listened to generals such as v Rundstedt, Guderian, Manstein, etc..he would have avoided most of the "first blizzard" losses, as well, which were the PRIMARY reason for the switch to weaker TOE..as a player, we perhaps have an unfair advantage already knowing that those generals were correct, but we should still have some way of not making the mistake, or at least, some luck involved, instead of automatically assuming we will make those mistakes, and programming into the game, that we will.
"chief idiot" Hitler implies that there were other idiots in Nazi and Wehrmacht leadership. And rightly so.
"60-65% of their effort in the east": From 1944 onwards "Wehrmacht" did not put a majority of effort & ressources into the Ostfront. The count is not only about manpower in the Heer. The air war alone in the Med (1942/43) and above the Reich (1944) was immensely costly in manpower and material. The Flak alone consumed gigantic ammounts of ressources.
"avoided most of the "first blizzard" losses": Barbarossa was everything bit the kitchen sink. Another short Blitzkrieg. There just was no plan B for any serious fighting after autumn, nor for the needed logistics. To have been forced to stop advancing would have been seen as defeat. Barbarossa wasn't fought in a vacuum but as part of a major war becoming a world war. German military thinking was all about "attacking is the best defense" and "do not fight on two fronts". Thus for Hitler and OKH it was imperative to go on.
Sure Overlord wasn't a sure thing, simply because it never had been tried before on this scale. But a successful German defense was even less a sure thing. Simply because the Atlantic front (from thes Spanish border to the North Cape) was thinly defended in many ways. (Apart from maybe the very first hours) the fate of Overlord was not decided by one lacking German division.