That moment of pure dread when QA starts using your feature in ways you specifically didn't account for in your test cases. You built it for users who follow logical paths, but QA's sole mission is chaos. They'll click buttons 17 times in succession, enter emoji in numeric fields, and somehow manage to crash the entire application by typing their name backward. The tears are justified—you knew this would happen, yet hoped against hope they wouldn't find that one edge case you silently labeled as "nobody would ever do this anyway."