We’ve all made mistakes. We’ve all done things wrong. We all know it. The important thing is what we’ve learned from those. It doesn’t matter what you got right or wrong, but what you walked away from that experience with and how you’ll use that information to your advantage in the future.
Over the last few years, even while things have been going well, I've made it a regular exercise to reflect on the last 6-12 months and write a brief "lessons learned" document, as if the startup was in fact a failure.
It's a fairly negative thing to do, and can be a bit demoralising, but every time I've come away with a useful insight.
It's also interesting how hindsight changes your "lessons learned".