"Oh, I am so silly, I forgot to add the same check over here."
*Narrator: There should in fact be no such check over there*
Today I spent two hours getting the full debugging setup working well, then an hour scratching my head and stepping through things until I finally realized that I should just revert that small commit from two days ago.
*Now* this can go live.
My unit test did not catch it, as it was not TDD and didn't test full boundary conditions and weird data.
Going faster always goes slower.