I like very much what Times classical music critic Anthony Tommasini says in an online Q & A when asked to give career advice to young musicians.
I think the same goes for actors, directors, you name it. So you make the substitution...
The musicians I knew back then who have managed to have stable careers are not necessarily the ones who were the most talented or the most ambitious. They were the ones who seemed the most content being musicians. The pianist always willing to play the first performance of a new chamber piece by a student composer, happy to have a work-study job accompanying the students of a voice teacher, ready to learn the piano part to the Hindemith Tuba Sonata (which is hard, let me tell you) to help out a tuba player preparing a degree recital. Young musicians who have that kind of contentment with their work, even while struggling, tend to fare well, in my experience. Whereas I have known other young musicians, sometimes formidable talents, who unless they saw a path to Carnegie Hall and a touring career became so frustrated that the pleasure of being a musician went away. Some just gave up.Either you get a break and get famous quickly. Or you do what you have to do to make it a profession, and all that entails.
Moreover you have to, on average, genuinely enjoy (or at least be "content" with, in Tommasini's words) the strictly professional gig, being the hired hand. Because that's going to be over 75% of the work you get.
Otherwise, you're just eventually gonna give up.