《管子·心术上》
必须懂得什么是不由自己去说的理论，不用亲自去做的事业，然后才懂得道的要领。
故必知不言，无为之事，然后知道之纪。
One must understand which theories one must not talk about, which careers one must not pursue, then one can understand the essentials of the Way.