As much as I love books I don't own every book I've read nor have I kept every book I've bought. Gasp! Is it sacrilegious to give away books? No, it isn't, and I will validate that when one is moving, it may be necessary to downsize. So how do you do it?
To cull your collection, I've named my method THE ONION ANALOGY.
Think of an onion with multiple layers. You peel them one at a time. You are now going to peel (discard) as the first layer all the books you don't like. You couldn't get into the story, it was boring, you liked it once upon a time but no longer. This layer is the easiest.
Then wait a day or two. Let your subconscious mull over the rest of the collection.
The second layer are books to "peel" are ones you read once or twice but don't have interest in re-reading them. Let them go. Again, wait a few day and move on to the last layer.
Finally, for the last cut of books is to ask yourself: IF I WERE TO GIVE THIS BOOK AWAY WOULD I CHECK IT OUT OF THE LIBRARY? If yes, it's a keeper. If you are one of those folks who tends to second-guess your decisions and later decide that you really wanted something, you've got plenty of options. You can order online, borrow it from a friend, go to a library, or use a Kindle version.
“Some stories are so familiar its like going home.”
- Louisa May Alcott