Yin and yang elements come in pairs—like moon and sun, dark and light, cold and heat, passive and active, and so on—but note that yin and yang are not static or mutually exclusive terms. While the world is composed of many different, sometimes opposing forces, they can coexist and even complement each other. Sometimes opposing forces in nature even rely on each other to exist. The nature of yin-yang consists in the exchange and interaction between the two components. The alternation of day and night is one such example: shadow cannot exist without light. Yin and yang can change under certain conditions, so it is usually not only yin and yang. In other words, yin elements can contain certain parts of yang, and yang elements can have parts of yin. This balance of yin and yang is perceived as existing in everything