Character background story my not be part of the world's background, but that doesn't mean you shouldn't talk about it in the beginning. You don't have to say much, just some basics. Of course, this is rather a matter of choice. I'm actually perfectly fine to be dragged into a story (which means not much background story about the world either!) without warning. Stuff can be explained along the way. But you should develop the plot in advance in any case or you will end up going back over and over fixing logical conflicts. I was lucky not to have gone away too far from my original idea while working on CP. I had to fix several pieces of the intro scene because the intro scene is very closely related to the main story which has changed since I started working on the game. As I said, I was lucky that it wasn't too much. I think that's what Dio was actually talking about.