My understanding is that Frank’s own father, Marty, was hard on him growing up, feeling this was the best way to prepare him for life in this world. Frank became so successful that he earned the respect of his father, a fireman> But he became such as big star that Jr was never able to live up to it.
Not to go too maudlin about Jr's troubles, billions of people wish they were him, but he genuinely loved the type of music that his father made. But just as he was becoming an adult, the Beatles and other groups thoroughly changed popular music and Jr was left with loving a form of music that was now a museum piece