What is the story?

We have lived in our house for exactly three years and have gotten to know most of our neighbor's fairly well. There is one person that we don't know well at all and for some reason I wonder what his story is. He is in his 50's and lives in his parent's basement. I know only a couple of things about his aside from the fact that he smokes acid cigars cheap and rarely leaves the house. We only know his first name and that at one time he had a wife and a child. No one ever comes to visit him and he doesn't have a job. Basically he only comes outside to smoke and that is the only time we see him. I wonder what has transpired in his life for him to be living in the basement and having such little interaction with the outside world. He could be perfectly happy with his life but I just find it a little odd especially given that he live right next door.