What’s the quietest failure you’ve ever tolerated at work?

I fixed the cooling unit Monday after three weeks of 'it’ll even out' from vendors and passive-aggressive tickets, only to realize the real problem was a labeled cable plugged into the wrong rack because someone thought 'PDU-A' and 'PDU-1' were interchangeable. Not catastrophic, just… slow, persistent, and embarrassing in hindsight. Do you have one of those? A thing you fixed and still cringe about?