To build up a library is to create a life. It's never just a random collection of books.
It is often much harder to get rid of books than to acquire them. They stick to us in that pact of need and oblivion we make with them, witnesses to a moment in our lives we will never see again. While they are still there, it is part of us.
For me the greatest joy is to be able to submerge myself for a few hours every day in a human time that otherwise would be alien to me. A lifetime is not enough.