2 reasons:

1. Hitler was convinced everybody around him was less competent. So his strategy had to be followed to the letter. In the beginning, able commanders such as Manstein, Rommel, Guderian took his orders, which were usually more like goals (mission-type tactics as opposed to orders-based tactics) and mostly achieved them. This led Hitler to believe in his superior genius. Sadly, many generals bought into his own myth. Even if some of it was down to dumb luck, and most of it due to his very able commanders. They even called him the Greatest Leader in War of all Time (GröFaZ - Größter Feldherr aller Zeiten). As the war turned against them, Hitler really had no idea how to cope with it and simply gave orders to hold position, even against all counsel. His commanders had achieved victory on their missions before, why wouldn't they now? A lot of them had to take the blame. The prime example is the battle for Stalingrad where Hitler got really angry that Paulus surrendered himself to the Russians instead of "shooting himself like a general of old would have killed himself with his sword"
2. Towards the end, Hitler really did reach a point where he wanted to sacrifice everything. His march-orders, better known as Nero-Decree, in particular show that he had lost all faith in the german people and army and was determined that, if he didn't go down in history for making Germany the greatest country in the world, he would go down for turning it to ash. Most of this is well-documented, the best analysis of Hitler's life and ideas is still the biography by Jochim C. Fest.