There is a strange phenomenon I have noticed with certain books. It is as if they want to belong to you; they can not be lost permanently. Lose them, try to give them away, they will return.
I've experienced two occasions of this happening. The first was the novel Volkswagen Blues by Québec author Jacques Poulin. I read it for a university class, and very uncharacteristically put my name inside the cover. Then I left it in one of the buildings at the university by mistake and it was gone. Three years later, now in a different university program and with different friends at a party, I struck up a conversation with a young man who as it turned out liked VW's. I mentioned this book as one he might enjoy; he said he had read it. Then he got a very funny look on his face and asked my name again. Turns out he had picked up my book three years previously and read it and given it to his father. His father sent it back to me. I still have it.
The second instance was a history of the Incas in Peru. I used it for a university class. Then I donated it to a library, where it was apparently sold in their booksale. At least three years later, I decided to study librarianship and began volunteering at this library. My supervisor was a slightly older man who I instantly had a crush on. Skip three years ahead; he and I are now a couple. I am browsing his bookshelves one day and what do I see? The same book, my old copy. We still have it.
I read the most startling instance of this in a letter to Victoria magazine from another second hand bookseller, some years ago. This bookseller had a small store in the US, and one day an older German woman came in. She browsed around, and after a while, the owner realized she had not seen her in quite some time. Upon searching around, she found her sitting in the children's book area in tears. She had a copy of Grimm's fairy tales in her hand, and explained that it was her own childhood copy, which she had left behind in the family home when they fled the Nazis approximately 60 years previously. Now there's a book which wanted to be found!