As reported at Salon.com, novelist Phillip Roth, 78, told a
French interviewer he is done writing. When he was 74 Roth re-read all of his
novels, starting with the most recent ("Nemesis") and working backward.
“I wanted to see if I had wasted my time writing,” he said. “And I thought it was rather successful. At the end of his life, the boxer Joe Louis said: ‘I did the best I could with what I had.’ This is exactly what I would say of my work: I did the best I could with what I had."
I think that’s a useful definition of success.