On one level, this is pure common sense.
On another level: how easy is it to say "so and so knows what they're doing, they've done this a million times, it'll be fine, I trust them."
Never. Not one time.
If you are the one hitching up your truck to a trailer - whether yours or someone else's - you do the last double-check yourself. Always. No ifs ands or buts.
Some years ago, I was hauling two horses to King Oak. Neither horse was mine. Both horses were owned by experienced owners and riders who had themselves hauled horses many times. So, I saw myself purely in the driver's role. I hitched up and presented my trailer; they put their horses and equipment on it. The drive was fine.
We arrived at King Oak, and the first horse unloaded just fine and went off toward her stabling. The owner of the second horse dropped the butt bar and asked her horse to back. He didn't. She asked several more times, growing more insistent, and then he backed. Hard. Fast. And...he broke his halter, because he was still tied to the trailer. The owner had never untied him.
He rocketed off the trailer and turned and in a split second I reached up and grabbed his nose with my right hand and pulled down. He was so relieved to have someone in charge again he stood quietly for me.
That was the occasion that caused me to make my first personal rule about hauling: I'm always the one to check the horses before we go, and the first to check them when we get there. Totally fine if owners help - in fact, I prefer that they do! - but before I put my foot on the gas pedal, or before I drop the trailer gate, I want to be personally, finally, reassured that all my equipment is correctly placed and functioning as expected.
So let me now tell you the second story that has sparked my new rule. I admit: I had a moment of laziness.
A few weeks ago, I used my truck to rent a car trailer from U-Haul and then used that car trailer to haul a 1978 VW bus back to work for a new thing we're doing.
It was a very long and very cool day and the moral of the story is that people should hire horse girls 'cause we get shit done, and we own the equipment with which to do it.
I arrived at the U-Haul dealership early in the morning, after having woken up and driven for nearly two hours, after not a whole lot of sleep. I let the U-Haul guy hook up the trailer because it was a type of hitch with which I was less familiar.
Obviously, I can do the chains and the electrical and all that jazz, but it was the coupler itself that I hadn't personally used a lot. So I let him do it, and then we tested the lights, and then off I went, driving another 1.5 hours north on a well-trafficked state road to get to the farm where I picked up the VW bus.
When we arrived at the farm, we had to unhitch the trailer for various space and logistical reasons. And the hitch would not come off.
It turns out that the U-Haul guy - who, one would presume, hitches up trailers all the live-long day, had not properly seated the coupler on the tow ball. Instead of sinking down and sitting home on the ball, then locking onto the ball, it had been perched on top of the ball and then the lock was engaged sort of...into the ball itself. So it was good and stuck. It took us 15 minutes of rocking the truck and swearing and jiggling to unstick it.
This is not a picture of the poorly done hitch; this is correctly done. See the brass colored piece just under the hitch? This is it correctly engaged in locking on to the ball. Now picture it about 1" higher and sort of biting into the ball itself. That's what I drove 1.5 hours with.
The trailer was unloaded, I never went above 50, and that coupler was good and stuck, but holy shit it could have gone so bad if I'd been going faster or hit a good frost heave. SO BAD.
I was speechless when we discovered what had happened. Thankfully, I was still sleep-deprived and under-caffeinated, so while I was able to react and fix things the real horror of it didn't really sink in that day and I was able to haul the 2.5 hours back home without incident.
Don't be me.
Be the last person to check your hitch, yourself. Don't ever, ever trust another person to double-check it. Not even people who should have all the expertise in the world. Learn from my dumb ass mistake. Though I had previously mostly followed this rule, it's now ironclad in my brain. My equipment, my responsibility, my final check.