http://www.internalfightingarts.com/

After many years of Tai Chi a small curve will look like ten million large waves going around.... Al Huang

At age 65, Master Jou Tsung Hwa wrote:
“There is no secret, no key piece of information which, if revealed, would instantly confer enlightenment and expertise. If you do not make progress, you cannot blame your teacher, because no teacher can transfer awareness to you. None of my formal teachers were famous taiji masters, and for over ten years I have not had a personal teacher. In that time I have discovered the only real secret: you must develop on your own. Anyone wishing to go further must be willing to re-examine the classical principles of taiji and intensify his/her efforts to embody them.” (From Camp Tai Chi blog How Much Should You Really Relax? by Walt)

6. Relax the waist
Source: http://www.taichizone.com/principles.htm
"These ten principles were developed by the great Yang style Master, Yang Chen-Fu, to help understand the movements of the form. The ten principles define a type of body structure rather than trying to dictate actual moves. They are regarded as the foundations of Tai Chi Chuan."