When I first studied martial arts (40 years ago) I was instructed to pull one hand back strongly to my hip or (in a few cases) abdomen. Pull it back strongly, I was instructed, to strengthen the outgoing hand. Every action has an equal and opposite reaction, Isaac Newton figured out. So, by pulling back strongly, I was to add force to my strike. I never questioned this, because I'm a sucker for science-themed explanations.
Years later, I met Sensei George Dillman. He said the withdrawing hand (hiki-te) is extremely important as a devastating component of pressure point techniques. "Watch this hand," he would quietly tell me whenever I asked him to show me a new point or a new knock-out. As a result, I now seek to be a student of hiki-te, an aficionado of the withdrawing hand. Enjoy this little video mini-blog.