《黄帝内经·灵枢·根结》
至于运用九针的玄妙关键，就在于了解经脉的起点和终点，所以如果能够懂得经脉的起点和终点，那么一句话就可以把九针的奥妙说完；如果不懂得终始的含义，那么针刺的理论也就要消亡了。
九针之玄，要在终始；故能知终始，一言而毕，不知终始，针道咸绝。
As for the mysterious key to using the nine needles, it lies in understanding the starting and ending points of the meridians. Therefore, if one can understand the starting and ending points of the meridians, then the mysteries of the nine needles could be said in one sentence; if one does not understand the meaning of the end and the beginning, then the theory of acupuncture will also die out.