Not learning from one’s mistakes.
I go through a cycle with my welding cover lenses. They get dirty and scratched and I clean them. They get worse and I keep saying that it’s not too bad. Eventually I get to a point where the weld puddle looks like an fuzzy light, change the lens, realize how clear things are with a new ($0.99) one and vow to never cheap out on cover lenses again. Then the cycle begins again.
It seems that I do this with kitchen knives too. I was touching up the edge on my trusty old Marttiini puukko and decided clean up a long-neglected carving knife for The Wife™. It cut OK before nut now it works as it should. I will never let a kitchen knife get that dull ever again. 😉