The concept of yin and yang has been around for several thousand years and it lies at the heart of classic Chinese science and philosophy. It is also one of my favorite in Chinese Medicine.
This popular symbol (to the right) represents the ancient concept. It illustrates the ebb and flow of yin and yang, light and dark, activity and rest, creation and destruction, it reminds us that everything is constantly changing. Also notice the dark blue dot in the white and the dot of white in the blue. These dots represents how even in the most yang there is a little yin and vice versa. Yin and Yang are opposing forces that are bound together and give rise to each other in turn.
This amazing concept can be applied to everything and everyone in the universe. Pretty cool huh?