My Dad used to be the same way. I finally got really mad at him one day and asked him. He said "Because I want you to be the best you can be." \n\nIt didn't make me like his nagging and yelling any better, but at least I understood why he did it, and I was better able to ignore it.  \n\nTruthfully, I secretly tried harder after that, knowing he wanted me to do my best.