Those who stuck with it have either discovered that they could make a living, or that they could enjoy making music as a rewarding hobby. A great musician has the right attitude. I rank attitude before talent, before technical ability, before practically everything else. I would rather work with a musician with slightly less ability, but a great attitude, than with a monster player who firmly believes that the world owes him stardom. That's another article in itself, but it includes respect for others, willingness to work at their craft and improve, and a sense of self-confidence.
Ability counts more than attitude.
A great musician never stops learning. To be a great musician is to be in school forever. The great Beethoven, near the end of his life, received as a gift, the complete works of Handel, a composer he had long admired. He would lie in bed and lean the books against the wall. As he read through the music, he would occasionally break into exclamations of praise and joy.