Internal Discipline is the most challenging aspect of learning Tai Chi. The central element of the practice dictates how a movement should be made from the internal core of the body—the abdomen and the back—not from the external parts of the body, such as arms and shoulders.
This discipline is essential to obtain the full benefits of Tai Chi. Without it the entire logical structure of Tai Chi disintegrates and can no longer be considered an internal martial art.
Tai chi is known historically as an internal martial art with a legendary reputation of cultivating neigong or internal energy and thereby achieving exceptional health benefits. Unfortunately, this art has been lost in most modern tai chi teaching.
Classical Tai Chi: "The art of Internal Motion that is mobilized by Internal Energy and directed by Internal Discipline"