This also speaks to a certain lack of inspiration/creativity. A lot of people who end up in graduate school are great at following a prescribed academic path and getting good grades etc. but when confronted with the prospect of original research might find themselves lacking. A lot of top scientists, like the great artists, writers etc. can't help themselves but think about or work on their field. Grothendieck disappeared to live in a cottage, but still produced thousands of page of handwritten notes of highly original mathematics.