Dao is a philosophy expressed in a book called Dao De Jing( Tao Te Ching) by Lao Zi which tells that everything has its opposite, like up and down, light and heavy, beautiful and ugly, strong and weak, fast and slow, good and evil, birth and death. The point is that the two sides are symmetric, no one is better than another. It is easy to understand that if there is no birth, there is no death. But it is difficult to think the opposite way. Actually they always accompany with each other. When one is giving birth to a child, you can say that the child is born, it is also ture to say that the child is dying. They coexist at the begining. The symbol of Dao is the YinYang map. There is always a black spot in white, a white in black. The harmony between the two opposites keeps the world the world. The most successful applications of Dao are (Sunzi) SUN TZU ON THE ART OF WAR, Taichi, and Chinese medicine.