Yin and Yang

From Wikipedia

Taijitu, the traditional symbol representing the forces of Yin and Yang

The concepts of yin and yang originate in ancient Chinese philosophy and metaphysics, which describes two primal opposing but complementary forces found in all things in the universe.

Yin, is sad, the darker element, is passive, dark, feminine, downward-seeking, and corresponds to the night;

Yang, is happy, the brighter element, is active, light, masculine, upward-seeking and corresponds to the day;

Yin is often symbolized by water, while Yang is symbolized by fire.

The pair probably goes back to ancient agrarian religion; it exists in Confucianism, and it is prominent in Taoism.

Though the words yin and yang only appear once in theTeo Te Ching, the book is laden with examples and clarifications of the concept of mutual arising.

The concept is a fundamental principle of Traditional Chinese Medicine.

Yin and yang are descriptions of complementary opposites rather than absolutes.

Any yin/yang dichotomy can be seen as its opposite when viewed from another perspective.