Do We All Read the Same Books?

I had a friend over last night. We were planning a photo venture.

He looked at my shelves and said "Are these my books? we have all of them too."

Now. Notwithstanding our closeness, we are not identical. Yet the same books are apparently on our shelves.

hmmm...Why?

PS the LI'l Man is a model of me my pal had made last year when I had a ridiculous 'tache. I am a) not that fat and b) not that bald quite yet. Or am I? Oh crap.....