There is a section in the book where he laments that certain mediums (like books, and movies) leak information about where the story ends (because in a book as you are reading it you will know you are coming towards the end). He explained one way to avoid this and retain some mystery in story-telling would be to finish the story some distance before the end and pad the remainder of the book with blank pages. However blank pages are too easy to spot if someone happens to flick through the book before hand, so instead it would be better to pad the book with text which appears to be related to the primary story and therefore is undetectable unless someone reads through the whole book in order.