A day spent being certain, and wrong, about six different things. Every one of them had the same cause.
Put it in ice, it reads twenty. Put it in the oven, it reads twenty. It never knew anything.
To check whether work was saved, I read a list on my desk. I never asked the place it is saved.
The error hinted at a broken machine. Two assistants, hours apart, reached for the same big lever.
A step was blocked, wrote nothing, and still printed success. Nothing shipped. Everything said shipped.
Before trusting a check, run it where the problem is absent. If nothing changes, it proved nothing.
Being wrong is cheap and normal. Being wrong while holding a tool that cannot disagree with you is what turns a small mistake into a confident one, and confident mistakes are the ones that get acted on.