"Normalisation of Deviance" is a concept that will change the way you look at the world once you learn to recognise it. It's made famous by Richard Feynman's report about the Challenger disaster, where he said that NASA management had started accepting recurring mission-critical failures as normal issues and ignored them.

My favourite one is: Pick a server or a piece of enterprise software and go take a look at its logs. If it's doing anything interesting at all, it'll be full of errors. There's a decent chance that those errors are being ignored by everyone responsible for the system, because they're "the usual errors".

I've seen this go as far as cluster nodes crashing multiple times per day and rebooting over and over, causing mass fail-over events of services. That was written up as "the system is usually this slow", in the sense of "there is nothing we can do about it."

It's not slow! It's broken!