Accidental uncoupling - dropping a trailer -

I would think that over 90% of accidental uncouplings come from high hitching where the pin box is high enough that the jaws closed under the pin or not fully around it. My DW has a tendency to raise the pin too high so I always double check and remind her that the truck needs to lift the front of the trailer a bit when coupling. But then, I have driven away with the stairs still out. :-(