Churn happened due to 24 hours clock

This is something that I have seen happen to another creator and it struck close to home for me. We had our timestamps being displayed in the browser locale, except for one export, which always displayed ISO timestamp as I coded this feature at 1am and never got back to it after that.

A person who works as an accountant in [country] canceled and said just one line about this in the exit survey.

One line of code. Many months of this feature quietly pissing people off without telling me.

I now maintain a list of "features I hardcoded when tired" and review them monthly. The list is longer than I'd like to admit.

What is the smallest and dumbest thing that has caused you to lose a customer? I'm quite sure there are more of those than postmortems we usually write.