Yin and Yang is a popular ancient Chinese concept of two complementary forces in the universe, which work hand in hand, to produce positive energy. Simply put, one force is positive or otherwise referred to as masculine while the other is negative or otherwise referred to as feminine. Neither is preferred or is better than the other, and both are highly desirable elements when it exists in perfect harmony and balance. This concept of equal balance between negative and positive elements is of course contradictory to most existing fundamentals where good is always sought after in its complete form.
The yin and yang concept however advocates the necessity of having both elements present to encompass an ideal balance. Relating it to a simpler understanding of hot and cold, where neither extremes are desirable but a combination of both, produces the warmth desired. Other basic ways of explaining yin and yang are, yin being soft and yang being hard, yin being stillness and yang being movement, yin being the sun and yang being the moon, yin being day and yang being night and so on.
