《黄帝内经·素问·徵四失论》
医道之大，可以比拟于天地，配于四海，你若不能通晓道之教谕，则所接受之道理，虽很明白，必反成暗晦不明。
道之大者，拟于天地，配于四海，汝不知道之谕，受以明为晦。
The principles of medicine are so broad that they can be compared to the heavens and the earth, and be commensurate with the four seas. If you fail to be well versed in the teachings of this principle, then the knowledge that you have acquired, though it may be very clear to you, will become obscure and incomprehensible.