is a rambling life lesson, that i once learned, and often ignore.
first without chi: stand upright. extend your dominant arm out, palm up (but in a fist). have your partner put the back of your fist on top of their shoulder, and they can rest both hands at the crook of your elbow. with every muscle in your arm tense, when they slowly pull down, they will be able to bend your arm.
next with chi: stand upright. extend your dominant arm out (on their shoulder), fingers extended, hand vertical (palm to the side), close your eyes and relax. say, "go". stay relaxed (only resist whatever force they're pressing on you). 