Tom Limoncelli:
You might be saying to yourself, "But Tom! I can't predict every precursor to an outage!" No, you can't, and that's a bug. That is a bug with the entire freakin' multi-billion dollar software industry. Any time you have a user-visible outage and you can't think of a way to detect it ahead of time: file a bug.
(from Stop monitoring whether or not your service is up!, emphasis added)