This sounds so stupid it might just be true.
A family bought their first boat. About a 20 footer with a 200 hanging on the back. They had never been in a boat much less operated one. They picked it up from the dealer and headed to the lake for their first outing. After getting the boat in the and feeling really good about their accomplishment, the Dad started giving it more throttle to speed things up. It seemed that the boat continued to flounder along and no matter how much throttle he gave it, it would not get up on plane.
Getting desperate, the family pulled into the marina a mile or so down from the boat ramp. After explaining the problem to the technician, everything was checked over and seemed to be operating as it should.
As a last ditch effort to find the problem, the tech went into the water to check out the boat's hull. He immediately exploded out of the water in disbelief and said, "No wonder, you still have the "*&%^$#" trailer attached to the boat."
They had apparently launched it by unhooking the trailer and rolling the whole rig into the water. True story? Maybe, maybe not.