In this clip, Master Chen corrected a common mistake in practice. Normally, people use one part of the body to accomplish two tasks. This causes the use of local power, which means you are using your hand to grab but also use it to make moves. This is an error in taijiquan practice. On the other hand, you should use global power (heli), which means that if you use your hand to grab, you have to use your elbow to pull or push.