About the "Guy who repairs cars but is a great guitarist" i think true great guitarists ( at least alot of them ) dont have jobs, other than something to do with guitar or music. They prioritized themselves right ( in my opinion ) and didnt get drawn to money. A great guitarist can leave it all behind and jump in the big pool. How often did Jerry Garcia have money before 1964? (when he was 22) not much! fact, he was livin in a CAR, sleepin in a car, for a few years ( if i remember right ). and i believe thats one of the main things a great guitarist must be able to do, put his priorities straight and have determination to do what he wants to do and not what others want him to do. If you look back in history, there are more great guitar players who are from middle class families than rich-snaubby families. Bob Weir came from a rich family, but hey, i mean He had a great deal of luck.

What im trying to say, is, to sum it up, is that you must be able to commit yourself to the instrument. If not, its just a hobby!