This isn't abstract theory. It's the rhythm of life:
They are opposites, like light and dark or fire and water. yin yang meaning shaded sunny chinese philosophy
Health is defined as the balance of Yin and Yang within the body's organ systems. An "excess" of heat (Yang) might lead to inflammation, while an "excess" of cold (Yin) might cause fatigue. This isn't abstract theory
Too much of one force naturally limits the other. If you work too hard (extreme Yang), you will exhaust yourself and get sick (Yin rises). If you rest too much (extreme Yin), you become weak and lethargic. Nature constantly seeks a dynamic balance. yin yang meaning shaded sunny chinese philosophy