* Germany lost world war 2 because Hitler when he invaded France, could have destroyed the rest of the British army at Dunkirk but instead he just sat there. and in North Africa Had Rommel Had more supply,tanks,men he could have easily taken Egypt. In Russia had Hitler not invaded the Caucasus Mountains and concentrated those forces in to the attack on Stalingrad thus taking the city and establishing bridgeheads across the Volga River, then driving onto Moscow. But of course Hitler invaded the cauces and the Crimea. This was unnecessary. This held even more units back frome the real objective Moscow.
Germany lost the war because Hitler didn't listen to his Generals, made decisions without thinking, and had no care for his troops.
The short answer, I suppose, is that Hitler ignored his own advice. In "Mein Kampf" he was critical of Germany's attempt to fight a "two front" war in World War I. In the Second World War, he turned around and did the same thing by attacking the Soviet Union. That was the beginning of the end. "Those who do not learn from history are doomed to repeat it."
Hitler shot himself in a bunker with his German Sheppard "Blondie" by his side