Ask HN: What's the worst you've ever screwed up at work?
Classic forgetting the full WHERE-part of a manual UPDATE-query on a production system. The worst part is you know you fucked up the nanosecond you hit enter, but it's already too late. Lesson learned? Avoid doing things manually even if a non-technical co-worker insists something needs to be changed right away. And if you do: wrap it in a transaction so you can rollback, leave in a syntax error that you'll only remove when you're done typing the query.