I ran across an interesting quote from Stefan Bucher, who has written a book called "All Access: The Making of 30 Extraordinary Graphic Designers." There's an interview with him at www.graphicsdesignforum.com. He was asked what was the big thing he learned from the process of interviewing 30 of the top graphic designers, and this is what he said:
"The main lesson I learned is that nobody ever arrives. None of the designers told me 'Hey! I made it. I'm on top and I'm feeling good about it. Time to kick back.' Each and every one of them still has some sort of monkey on his or her back. Despite years of success, most still have to work for a living, and they all crave new challenges. The journey doesn't end until it's ended for you. Is that discouraging or heartening? A little of both, perhaps."
I think the same applies to writers. I can remember before any of my scripts were produced, I thought "success" meant having your writing actually shot for TV or film. After a while, I re-defined it to having your script shot pretty much as you'd written it. Then, shot as you've written it and featuring good actors. Of course, the more conditions you attach, the less frequently they are met.
Not only do the goal posts move, but we're the ones moving them. The funny thing is now I've gone full circle--or beyond. Now I define success as enjoying writing the first draft...after that, anything else is gravy!