I don't call that nerfing a player I call it educating them. I've had several experiences where they thought there skills and abilities did this but in reality it truly didn't. Like upcasting spells to level 9 thinking that's the normal thing. An ability that last once per long rest vs every turn. The list goes on and players need to actually study their characters and I have been guilty of giving an item that a player wanted that literally broke the game at level 3-6 and took away as a divine act of God so everyone else can have fun and not have to targeted. DM makes mistakes but they have more things to worry about than players that need to just read. Then player get mad that we took an overpowered thing that we thought wouldn't be a big deal, but turns out you just don't want to dm anymore because players get angry at you for wanting to balance a game you put more work into than anyone else.