Their is an episode of Seinfeld in which George wanted Jerry to get his book from his now ex-girlfriend and later in the episode after Jerry got stuck being the girls new boyfriend he asked George why he wanted the book since he had already read it.
If people don’t understand why you would re-read a book in which you already know the ending, then I would ask why do you keep your music, movies and tv shows on dvd? You already know how the movie ends. You have seen Sixth Sense and know the big ending, so why don’t you throw it away, give it to charity or sell it? Because you enjoyed the movie and want to watch it again some other time.
That is how we feel about our books. I could be watching something on tv and suddenly remember a scene in a book I enjoyed and then I could spend hours in frustration looking for that book and when I find I read it all over again. There are also some books that I have, that I may not have read in more than a year and I have forgotten some or most parts of it and it’s like reading it for the first time all over agian.