The center can't hold

The two complimentary forces of life in Eastern thought are yin and yang. Yin is conceived as earth, female, dark, passive, and absorbing; it is present in even numbers, in valleys and streams and is represented by the tiger, the color orange and a broken line. Yang is conceived of as heaven, male, light, active, and penetrating; it is present in odd numbers, in mountains, and is represented by the dragon, the color azure, and an unbroken line. The two are to proceed from the Supreme Ultimate, their interplay on one another (as one increases the other decreases) being a description of the actual process of the universe and all that is in it. In harmony, the two are depicted as the light and dark halves of a circle.

Simply substitute liberal and conservative or Democrat and Republic for yin and yang. Voila! The world of politics stripped bare as our Western concept of darkness and light is applied. But a major problem immediately arises. Why do not the two parties complement each other rather than function as diametrical opposites? Why do not the two parties form a tense but unified whole? Why does their unending interplay never synthesize for the common good of America?
Perhaps the center of the circle cannot hold?