Q: Tai Chi seeks to be supple but what is the use of suppleness?
A: Seeking suppleness enables you to separate your body into pieces. If an opponent pushes against your forearm, your elbow doesn’t move; if against your elbow it moves, but not your shoulder; if against your shoulder it moves, but not your body; if against your body it moves but not your waist; if against your waist it moves but not your leg. This process leaves you as stable as a mountain. When you discharge your opponent, then it is from the feet through the legs to the waist, body, shoulders, elbows, and hands – all connected as one unit, discharging energy like an arrow toward its target. If you cannot relax, your whole body becomes one piece and, even though it is strong, a stronger person will be able to push your one piece and cause you to be unstable. Thus the use of suppleness is crusial. With it you can be one unit attacking and fragmented parts defending – able to be relaxed and hard, agile stepping forward or back, and substantial and insubstantial as needed. Whit these abilities you will then have all of the Taichi function.
Reference: T’Ai Chi Ch’Uan Ta Wen, Questions and Answers on T’Ai Chi Boxing Chen Wei-Ming ( Benjamin Pang Jeng Lo & Robert W. Smith ) North Atlantic Books 1985