You can learn more from failure than success. In failure you’re forced to find out what part did not work. But in success you can believe everything you did was great, when in fact some parts may not have worked at all. Failure forces you to face reality.
Fred Brooks, Fred Brooks Shows How to Design Anything (via wka)
I’m reading The Design of Design right now and find myself wanting to quote everything Fred Brooks says. I think he qualifies as one of my personal gurus.