How quickly it can go badly wrong when hitching/unhitching

[Steph and Dud B]

Scary scenario. From what I gather, the man reached under his Anderson leveler to pull it out and the truck/trailer rolled a bit, probably from the play present with the parking pins in an automatic transmission (I know my truck can move an inch or two before the parking pins engage.) This is why you never put your fingers underneath anything that could take a load (tires, jacks, cribbing, etc.). Also why I always walk back to the cab of my truck to verify it's in Park and the brake is set before I lift the trailer off the ball or pull any chocks. In addition, I double check the chocks and leave the safety chains on when I lift the trailer off the ball. I did have a truck/trailer combination start to roll on me once because I forgot to put it in Park. We also once had a "toad" car behind a neighbor's motorhome roll across the road and hit our trailer when they forgot to put it in park before unhitching. Large vehicles moving unexpectedly is very scary. 

https://blog.campingworld.com/lifestyle-activities/you-need-to-hear-this-story-before-you-go-boondocking-all-alone/