《黄帝内经·素问·刺法论》
黄帝问道：人体虚弱，就会使神志游离无主，失其常位，从而使邪气自外部干扰，因而导致不正常的死亡，怎样才能保全真气呢？
黄帝问曰：人虚即神游失守位，使鬼神外干，是致夭亡，何以全真？
The Yellow Emperor asked: when the human body is weak, the spirit will be wandering and has no master, and it will lose its normal position, which will cause the evil spirit to interfere from the outside, and thus lead to an abnormal death. How can the true qi be preserved?