Neil did not make sufficient progress at Texas. Then he did something weird, where he wasn't ready to defend yet got a postdoc at (iirc) Princeton. Princeton had to rescind the offer because you (ahem) need a doctorate to be post doctorate. Then he got into Columbia's program and finally finished.
He had a lot of hobbies and interests other than astronomy, and he is actually a very smart guy, but it took him a bit longer to get his shit together. I think he's found his calling and is quite good at he does.