Harder not to move

Stephen Hwa, p. 50 Uncovering the Treasure " To be able to keep part of the body still, by itself, is also important training to eliminate unwanted habitual motions (some disciplines call the unwanted habitual motions "Parasitic movement") 

"Sometimes it is more difficult to train students NOT to move than HOW to move" For example is Yin/Yang pairing of the quarter body: "Burst of energy" or "Fajing" impact force of a strike or punch then equals the amount moved in the desired direction by 1/2 of the "pair" minus the force generated by not moving the muscle of the other 1/2.