Virtue
There were virtuous men who capitalized on the principles of Heaven and Earth, derived their life principles from sunrise and sunset, from the waxing and waning moon, from the arrangements of stars, from contradictions and harmony of Yin and Yang, from differentiation of the four seasons, endeavouring to arrive at the principles of life which are in harmony with their ancestors of ancient times. And, by this way, they were able to live as long as possible.
-The Yellow Emperor’s Classic on Internal Medicine