You're on the Titanic and it's going down. You have mere seconds to get out of your cabin and onto a lifeboat. The crew aren't going to let you save all the books you brought with you - they would need an entire lifeboat themselves! - but you may be able to smuggle one out inside your jacket.
The trouble is, which one do you save?
PS. To clarify, just because you're on the Titanic, doesn't mean you're limited to pre-1912 books...