I think a lot of his ideas were formed in the context of a sense that he was always protected from consequences. No chance of failure in school, no chance of getting drafted, and he had such a comfortable cushion after failed business ventures that they were barely even detectable.
Thin skin, not caring if what he says offends people, and a belief not only that he would be a successful president but that his uniformed opinions are enough to make it so are an entirely natural set of beliefs for someone who has not ever faced criticism or real fear.