Why was Hitler blind?
Adolf Hitler was not truly blind in a physical sense. In other words, his eyes worked fine. Therefore, I wonder if you are asking this in a metaphorical sense. Metaphorically, Hitler's major blindness seemed to be a blindness to common morality and to the idea that he might be wrong about things. We can say Hitler was blind to morality because he was willing to do horrific things like killing the Jews and many others who he saw as inferior. We can say that he was blind to the idea that he might be wrong because he was arrogant enough to overrule his generals and other advisers on a regular basis. In these ways, though not in a physical sense, Hitler was blind.
Actually, Hitler was blinded temporarily during World War I. He had left Austria to avoid the draft there, but then volunteered in the German army. On the front he was employed as a runner to carry messages when communications lines went down, which happened rather frequently. On one occasion, he was caught in a mustard gas attack, and was temporarily blinded as a result. He was promoted to the rank of corporal--the highest military rank he ever held--and awarded the Iron Cross for valor. His blindness was only temporary; but made him a hero. Ironically, Hitler never made great mention of his injury in later years.