Family sometimes send me packages unannounced, not all shippers (especially international) give real-time tracking numbers, not everyone in our household keeps perfect track of their inbound shipments, and sometimes delivery agents just make a mistake - one time I came home from work to a big screen TV on my porch. It was supposed to go to neighbor, but that's something I wouldn't want on my porch for a week - even if I don't care if it's stolen, it's like a big "No one is home here!" sign.