I don't know a whole lot about motivating a young person to change their attitude, but I know some parents who need to give their kids two weeks notice and reserve a moving truck. I know somebody who did that. They told the little 20-something, "We can have your stuff moved into a place you found to live or we can haul it to the city dump. That's your call, I suggest you get moving."
CC&E
A number of years ago when I was a young man living at home and working full time mind you... I came home one day to find all my stuff packed up in boxes in the garage. At the start of the next month I was in my own apartment.
My kids are 16 and 11. A girl and a boy. They both know that when they graduate from college they are expected to live their own lives. Do they find it scary? Sure. But you know what? So did I when I was 21 and just out of college. They'll survive -- and they'll be better off for it.