The Tao Te Hsien is the wisdom of a priest named Hou Ti as relayed to Hanuman then written down by T'u, Komuko guardian of the Library of Earth. The Tao Te Hsien is both philosophy and magic; a means by which the Shinma believe they may return to the spirit worlds.
The Hsien of Japan have created a Zen-like version of this called Hsien-do.
One day Hanuman met a mortal priest, a wise man named Hou Ti, who was having a bad day. He was traveling through the mountains seeking wisdom when he had run into a Kuei-jin seeking food. The poor priest was wise but no warrior. The Kuei-jin fell on him and he would have died of Hanuman had not decided to intervene. The monkey king killed the Huei-jin, not because it was his duty to protect the monk (which it was, as much as he may have refused to admit it) but because all the Kuei-jin were responsible for Hanuman being in his present predicament, namely being stuck in the body of a human and separated from the Celestial Courts. If the Cathayan had done his duties to the August Personage of Jade, Hanuman would have continued minding his own business instead of being stuck in a body that refused to do what he wanted it to do. He hated being inconvenienced and made his point by taking his enemy's head.
Of course Hou Ti was very grateful and fixed food for his new friend. They decided to travel together for a while and between stories of Hanuman's craftiness and courage, Hou Ti told tales of the Taoist Philosophies and for the first time in his life, Hanuman did more than talk. He Listened. And he Learned.
While they had may adventures together, eventually they parted ways, but not before the Monkey King had learned certain things. One was that no creature should endeavor to be all Yin or all Yang. Only a balance of the two could bring harmony to mind and body. With this revelation, Hanuman realized that the Great Wall placed between himself and the Heavens was not as solid as he thought. He discovered doorways in it and with this understanding a jade key appeared on his tail.
As the Hanumen tell it (just like the Monkey King) if any other Hsien had found the secret all would have been lost because the infighting had grown worse and few had proper defenses. On the other hand, another shinma would probably have shared the information before immediately using it to get in trouble.
Hanuman, like any Monkey, promptly entered Heaven, heading straight to the Orchard of the August Personage of Jade, and ate the Peaches of Immortality; a fruit saved only for the very wisest whom Heaven wanted to honor with such a gift. The August Personage was obviously upset by this but couldn't change the fact that Hanuman was now immortal. Still, the Monkey King was cast back to the Middle Kingdom and the matter considered closed.
Had Hanuman not eaten the peaches the knowledge he had gained would have been lost. Instead he retained the secrets he learned and, being a bit of a braggart, immediately set about bragging about his great deeds. He told his tales to T'u, the Komuko Guardian of the Library of Earth and to about a thousand others who could be bothered to listen.
T'u fortunately wrote down the knowledge in his wisdom and began sharing the secrets of Tao with other Hsien and the venerable Komuko has long since ascended to perfection. Hanuman could be anywhere but is probably still getting in trouble. The knowledge the one gained, though, and the other shared, saved the shinma from certain doom and allowed them to continue their quest to serve Heaven.