Its very rare that I do anything wrong when it comes to boating (LOL), but one time several years ago I had a Mach 26 with a HP500 and offshore hand controls.

While tied up at the dock, a dock line pushed the throttle almost wide open (boat not running) and I did not notice. I fired up the boat and it hit 4000rpm instantly. Scared the absolute shit out of everyone on the boat including me. So within milliseconds I hit the throttle (actually the shifter) forward. The boat died. When I figured out what I did I reset everything and refired the boat. Started right up. Put it in gear and nothing.

I ended up shearing the lower main shaft. It looked like it was made that way, the upper portion had a beautiful twist in it. The lower portion was cut clean in half.

Thankfully no one was hurt, except my wallet