I asked one of my seniors once to show me how katate mochi sokumen iriminage ni really worked. During class I just couldn't figure out how it could work.
So he put his hand out, and asked me to grab and push. So I did. He stood there looking at me, and again asked me to push ... harder. So I did. Then he asked me to REALLY PUSH...
When I woke up, I still didn't know HOW the waza worked, but I was no longer doubtful that it did indeed, WORK.
My senior was nidan then. Now I am nidan. I still don't think I'd want to be on the recieving end of the head instructor's full power, full speed waza...and he's pretty good at taking care of uke. But full speed and power...yikes, no thanks. 2 herniated discs in my neck is enough, thank you.