Usually my fault for one reason or another but you know, cutting steel especially, is not easy on cutting tools and cutting tools are consumables. Sometimes we "consume" them faster than others - I think a lot of the time, it comes down to rigidity (or lack thereof).
I sometimes shake my head at some of the old "toothless wonders" I sometimes try to make do one more cut.
And Aluminum: I've got a kind of "Love / hate relationship there - I love how it cuts and how much better / longer tooling life I get with it but I use quite a bit of WD40 as coolant / lube on it and hate how chips get stuck to everything.