They oppose each other and at the same time cooperate with each other, thus a relative balance is maintained between generation and restriction, and the normal growth and development of things is ensured. Should one of the five elements be excessive or insufficient, there would appear the phenomena of abnormal restrictions, known as subjugation and reverse restriction. By subjugation is meant that one element subdues the other when the latter is weak. It is the manifestation of abnormal coordination among things. For instance, if wood is in excess and metal can not exercise normal restriction on it, then the excessive wood will subjugate earth in such a way that earth will become weaker.
Reverse restriction means preying upon others.
That is, when any one of the five elements is in excess, the one originally restricting it will be restricted by it instead. That is why we call it reverses restriction. It is clear that the order of reverse restriction is just opposite to that of restriction and that reverse restriction is undoubtedly a harmful one. In the science of TCM, the theory of five elements is used, in the main, to explain the physiology and pathology of the human body and to guide the clinical diagnosis and treatment. The generation of the five elements can be used to expound the interdepending relations between the five viscera.