I've seen things that no one would believe, saw a guy put his boat...
on the trailer, yell for his son to pull the truck up without hooking the front rope and the boat fell off the trailer about 6 feet from the water, dad still sitting in the boat drivers seat. Nice 20' or so ski boat sitting on the ramp and the guy and his son yelling at each other. Saw a bass boat guy do the same thing after he put those slick pads on his trailer bunks and didn't realize how slippery they are. A boat will glide right on the trailer, unfortunately, it will glide right back off.
More plugs left out than you can count and more boats floating away with no one in them too. I'm convinced a lot of people buy nice boats and have never backed a trailer in their life, it's comedy gold watching them zig zag their way down the ramp and usually off one side and get the trailer axle stuck on the rocks or edge of the concrete ramp.