In Chapter 4 of 16 of his 2009 Capture Your Flag interview, entrepreneur Joe Stump provides a practical view answering "What defines success in what you do?" by comparing internet architecture and programming to structural engineering. He concludes success means "Not breaking things."
Erik Michielsen: How do you define success in what you do?
Joe Stump: Not breaking things. At the end of the day, it is an engineering field. How does an engineer describe success after he has built a bridge? It didn’t fall down. So, I mean at a core level, you do everything you can to not break stuff.