"Self-Refinement" ( 煉己 Lianji ), a term of Inner Alchemy ( 內丹 Neidan ), means to banish distracting thoughts and concentrate one's attention on cultivation. It just refers to the cultivation of the mind and one's spiritual nature. Daoism regards Self-Refinement as a preliminary step. Zhang Sanfeng, a famous Inner alchemist of the Yuan and Ming dynasties, pointed out in the Essentials of the Mysterious Dao ( 玄要篇 Xuanyao Pian ) that "the cultivation of one's spiritual nature should precede the cultivation of the Reversion Elixir ( 還丹 Huandan ), and the cultivation of the mind should precede the production of great elixirs." It shows that Daoism attaches great importance to "Self-Refinement". The mind of a mortal is easily subjected to outside enticement and attraction. In Daoism, this restless mind is called “a heart like a capering monkey and a mind like a galloping horse". The impetuousness and perturbation of the mind are regarded as a root of the harm to the human body. A practitioner of Inner Alchemy first cultivates and concentrates his own mind in order further to adjust his breath so as to empty his mind and achieve the state of holding no spirit to be concentrated. It is difficult to stabilize one’s mind. Our predecessors controlled their mind by “drooping the eyes, looking at the nose, and listening to the breath”. "Drooping eyes” means drooping one’s eyelids, "looking at one's nose"means paying attention to the tip of one’s nose, and "listening to one's breath” means listening to one breath attentively. This way of control is one of "Interfering Action" ( 有爲 Youwei ). It aims at restricting the impetuous thoughts "with other thoughts". However, one has to banish all the thoughts in the end in order to enter the active state of Inner Alchemy.