I've been thinking about the different ways that books can feel like they're yours. They resonate with you in a very specific way so it feels like they're part of your identity.
Some books are yours because you loved them in childhood, and whether or not you still enjoy them, they remain in your memories as something that formed your personality.
Some are yours because you found them on your own and you love it so much that you're almost afraid to recommend them because other people won't love it the same way. Or you almost get jealous that other people like them because those books are yours.
Some are yours because you're the only person you know who's ever read them.
Some are yours because you spend a lot of time thinking about them.
Some are yours, because even though they are wildly popular and were popular before you ever discovered them, and there are plenty of people who like them much more than you do, the way or reason it resonates with you is very specific to you and no one else can replicate that.
These'll often be your favorite books, but not always. You can like something a lot but not have it be part of you. You can think the book isn't that great, but something about it resonates with you and sticks with you forever. There's something very specific and personal about the books that are yours.
This should be a challenge (!)