That is a quote by Arthur Rosenfeld, considered by many a Tai Chi Master. His book “Tai Chi: The Perfect Exercise” is probably a must read for Tai Chi folks. I certainly agree with his statement.
There is a dicussion of his book on this site which also lists links to many other Tai Chi resources, including very impressive videos. Violet Li is a Chen practitioner so there is a strong Chen bias and mostly Chen Style represented.