I know almost all of us have been told, some way or another, to always make sure you have at least 10% of the trailer weight on the tongue. For those of you who like clean underwear and don't want to experiment on your own to see what happens if you don't follow this rule, U-Haul has created a great little demo. Me and my dirty underwear can attest to the accuracy of the demonstration.
https://www.uhaul.com/Articles/Tips/8335/How-To-Request-Your-Own-Safe-Trailering-Demonstrator/
https://www.uhaul.com/Articles/Tips/8335/How-To-Request-Your-Own-Safe-Trailering-Demonstrator/