I worked at a shop during the original mountain bike boom of the 1980's. Bikes didn't have replaceable derailleur hangers back then. We were constantly bending the tabs back oh so gently from sticks in the der. Sometimes they would crack and we would have to have the local frame builder put in a new dropout. Which is now the reason why all mountain bikes have replaceable tabs now. Not as common on the road, but stick in the der is always a bad thing.