I had a cousin with a similar mindset. He lacked one year of finishing his degree before getting drafted. Somehow the Army removed any desire for him to finish his degree. The remainder of his life was spent living at home doing odd jobs, working in garages or bowling alleys, etc. His brother, just as intelligent, finished his doctorate and became the head of the chemistry department at a major university.
Emotional trauma and PTSD of military experiences can do that.