All it takes is one time and you could lose your life. I've seen all kinds of things. Leaking hydraulics and a slow crush, I also watched one guy lower a small RV while kneeling on one knee. He dropped the bumper on his other knee so the full weight went straight down from his knee to foot, splitting the shin bones. Gotta think about what could happen, and then make it impossible.
Situations can go pear shaped in an instance.
My first engineering job was designing dump boxes, snowplows and salt spreaders for large trucks. I would sometimes cover our technical support department when they were busy or out. I got a call one day from a dealer of ours where a guy had been killed installing one of our dump boxes onto a truck.
Our manual said to put 8”x8” or larger timbers across the truck frame while working under the dump box. This provides a “livable” amount do space should the box drop while a person was leaning across the truck frame rail due to a Jack or hoist failing.
Turns out this particular guy was hooking up the air cylinder for the tailgate release while he was supporting the box with an over head hoist. Unfortunately, the hoist was hooked to the tailgate so when he hooked up the air, the tailgate releases causing the tailgate to swing up and the box drop. Since he didn’t have a timber in place he was crushed between the dump box and the truck frame. They knew when they lifted the box he would immediately bleed out internally so they had his wife come in to say good bye before they lifted the box. He was 29 years old.
I don’t mess around with anything that isn’t supported properly.
