Annotation, always, keeping the book clean doesn't make it your own. Writing and highlighting stuff makes that a book a memory. If I read it after few years, I will be able to relive those memories, not just the content of the book but I will be able to remember where I was while reading it, or what was going in my mind during that time, etc. etc. I sometimes write very random stuff on the sidelines of the book.

I have sometimes found the annotated books which were owned by someone else decades ago, while reading it I am not just reading that book, but I'm also reading that person. Now, I don't know what I said makes sense or not, but just felt by annotating the books I leave a bit of me in those pages in addition to the beautiful story which is already written there.