In Taoist doctrine, Heaven, Earth, and Man all possess the Three Elements.
Heaven's Three Elements are the trinity of Sun, Moon, and Stars.
Earth's Three Elements are the trio of Water, Fire, and Earth.
And Man's Three Elements are Essence, Qi, and Spirit.
Born with Three Elements, both vast Heaven and Earth and people are, from the very beginning of their birth, in a continual process of depletion and consumption of the "Three Elements."
The depletion of the Three Elements of Heaven and Earth is apparent in the changes of sunrise, moonshift, and landscape rivers; compared to the puny human power, the depletion and consumption of Heaven and Earth's Three Elements are evidently too immense, human power cannot alter or match it, hence it is called the "Great Three Elements."
Therefore, the only thing a person can grasp is their own "Small Three Elements."
