Hmm. I voted for "making a living," because I think I'd call any other writer successful who did that. If it's just getting published, I've done that. If it's having strangers say something good about me, I've done that. Despite my very limited publications I even twice had a total stranger know who I was. I had a lit student email about an analysis of one of my stories she did for a lit class. So if those are "succeeding," then I've succeeded, and so why not quit? They must not be, then, entirely satisfying me.
After I had written fiction for 12 or 15 years, published for four years fewer, I wrote a long letter to my grandmother, reminiscing about our times together, including describing this odd thing she used to do with my grandfather at the dinner table, where she'd put some bizarre object on the table to see if he'd notice (like a bottle of bleach or a coiled garden hose), proving that he didn't notice much. And we'd laugh about it together back then. As an adult, writing about it, I wondered if he didn't actually notice, but decided not to engage her wrath (she was a spunky little thing!) by mentioning it. A few weeks later, my sister phoned and said my grandmother had said I must really be a good writer, because the last letter had made her cry. And I thought, you know, maybe this is the only really important reason I've learned to write this well, so that I could thank someone I really did love to bits with the writing. She died two years later, and I still miss her lots. Everything else seems like icing, really, after that.