“One will remain strong if he has the knowledge of nourishing life and one will grow old if he has no such knowledge which accounts for the fact that some are stronger than others although all of them are born with the same energy of Heaven and Earth.
“A man of wisdom will examine the common principles of nourishing life and obey them but a fool will not act until the symptoms of disease and weakness present themselves. As a result a fool will always be short of energy whereas a man of wisdom will always keep his energy in abundance and when his energy is in abundance his ears will hear and his eyes will see clearly, his body will be light and strong, an old man will retain his good health and a healthy person will become as strong as ever.
“This is the reason that the Sages will do nothing contrary to the right way of nourishing life; they enjoy a simple life as well as a quiet life with the result that their longevity becomes unlimited and their lives end with the Heaven and the Earth. This is the way of nourishing life as practiced by the Sages.”
-Huang Di Nei Jing, Henry C. Lu