Just a few weeks ago, we saw a group of teens launching a 20' speed-boat. They forgot to untie the bow line to the trailer and were head-scratching as to why it wouldn't float off the trailer.
They'd actually unhitched the trailer from the truck and pushed it further out into the water. Guess what happened next - someone realized the bow line was still attached and untied it. They and a couple of SCUBA diver buddies spent the time the kids should have been out on the boat, diving down to get a line on the sunken trailer to pull it back onto the ramp.
There were a lot of ticked-off boaters waiting to use the ramp.