Since moving to a weight distribution hitch it has become impossible to get this wrong. I use side-mounted chain hangers on the trailer frame so I have to use the trailer's jack to lift the tow vehicle enough in back to engage the chains. This is an absolute positive test that I'm coupled and latched. But I have seen many times on many trailers where the coupler latch can be closed without being properly seated. I understand these things are in use all the time, around the world, every day. But there's a bit of a design flaw if they can appear latched and not actually be.