One of the least intuitive aspects of Sun Tzu's system of Sun Tzu's strategy is what we call "complementary opposites." According to bing-fa, all of nature exists, not as a steady state, but as a tension between opposing conditions. The climate and the ground, strength and weakness, offense and defense, male and female, emptiness and fullness, standards and innovation, group action and individual decision, knowledge and ignorance are all complementary opposites. Each condition not only creates its opposite but is a necessary condition of its opposite.