To me, being successful means...
Earning a living by doing what makes me tick. It makes me happy to be in my profession, and yet I would do it anyway, even if I had to earn my living some other way.

My definition of success has not changed over time. 
I'm a musician/educator/performer. If something isn't working, I always have another opportunity. People like me are always "auditioning." Every job we do is a resume for the next job.