Through observing nature, living organisms and the human body over millennia, who we call the Taoists observed that there are many types of “I” in the body and more importantly (in this context), three layers.
Without giving them a label, the Taoists are simply humans wanting to live in accordance with nature and to be as healthy as possible. This wisdom and grassroots scientific observation led to the quintessential theory of Chinese philosophy that is known as The Three Treasures.
The reason tonic herbs are tonic and so revered, is because they work on balancing, harmonising and building these Three Treasures; they are historically the herbs seen to cultivate health and longevity with the most efficacy.