You must know everything well before you can know what to discard.

You must know everything well before you can know what to discard. You must cover pages with material you will not finally put into the book. That doesn’t mean you don’t use it. It is still there, must be there, an invisible foundation which gives authority to the story. The planning done on setting is never wasted. Nothing is ever wasted. If it has been thought through and written, it is still there, in every word which does not mention it.