My suitcase simply failed to appear on the carrousel one time. After it was clear no further bags were coming, I contacted airline official, who gestured to a suitcase standing alone near the entrance to the baggage area. Was that my suitcase?
It was. Airline official explained that sometimes baggage headed to city "X" is loaded into a plane that departs before the passenger's plane to city "X", and when that happens the airline takes the baggage to the carrousel where the passenger's plane's luggage will appear, and leaves at the entrance, so that the passenger may pick it up without waiting.
Great. But how was the passenger supposed to know that, and not spend an increasingly frustrating 45 minutes watching the luggage carrousel for a suitcase that is never going to appear on it? "Oh", airline official replied, "everybody knows that." So now I always look for unattended bags near the luggage carrousel, in case mine caught an earlier flight.
My duffel bag hit the carousel about a half hour after everyone had left...no flights in between. It was like the airport was closed, and it was likely one of the biggest in the country.