A book deserves to be on this list if it fits these described criteria:
I'm talking to a friend and we discuss books. I ask them if they have read Such-and-Such Book and they say no. Oh, but you must, I tell them, and I promise to bring it for them to read. When I get home I immediately locate Such-and-Such Book on the shelf, but instead of putting it by the door to go with me next time I leave, I cannot restrain myself from sitting down on whatever is closest and opening it up and looking at the first page. This reminds me why Such-and-Such Book is basically one of my favorite things in the whole world, and I then can't loan it to my friend because I have to read it again first. For this reason I have two copies of some of these books.