My best learnings came from mistakes - mine, my team's, my company's, other companies - but almost always, it was when those mistakes were promptly followed up with a thoughtful incident report.

For example, when I launched what is now Uber One, two days later, I got a call that I broke something. It turned out I had forgotten an edge case in a completely different service. Yes, this was 2016 Uber, 3000 microservices, but I don't think the users who didn't get their discount really cared.

The takeaway I still remember from that today is about always looking for "works by coincidence"; I often ask myself about the preconditions that must be in place for some class of mistake to be impossible.

The framing of preconditions that dissolve a class of mistakes is intriguing. I keep re-reading it, trying to picture how it actually exists day to day: is it something you run in your head when you're in the code, or is it structured into something your team shares (e.g. a checklist or similar)? I haven't had much success closing that gap.