Even the people of old needed to be reminded of the Way of Health. In a conversation between the Yellow Emperor and his assistant, Qibo, we are reminded of what it takes to lead a healthy life.

"The people of old, they understood the Way,
They modelled themselves on the Yin and Yang
And were at peace with the arts of destiny.
Their eating and drinking were in moderation,
They rose and retired at regular hours,
They neither had wild ideas, nor wearied themselves out at work.
Thus they were able to keep body and soul together
And so attain the end of their natural span,
One hundred years and then pass away." - from Essential Texts in Chinese Medicine: The Single Idea in the Mind of the Yellow Emperor (Kindle Locations 1031-1037) by Richard Bertschinger

The Dao, or "The Way," means to follow Nature. The Dao can be understood through the manifestations of Yin and Yang. If we are to live in harmony with Nature we must adhere to those rhythms otherwise we will cut our lives short.