Patron: So what happens if I come in with books I got from another branch, but I don’t have my card?
Me: You would need to return them.
Patron: But that’s not fair! What if they were mine?
Me: What if they weren’t?
Patron: You don’t understand. If these books were my property, and you took them, that’s a crime.
Me: You’re right, it would be. Except they’re never your property. They are ours, and we are letting you borrow it under a set of explicitly-stated conditions.
Patron: You don’t get the point I’m making. That’s discrimination! This is criminal!
Me: I don’t think you know what those words mean.
Patron: These are my books!
Me: Buddy you have your card, why are you even complaining
Patron: IT’S THE PRINCIPLE OF THE THING