《资治通鉴·唐纪·唐纪四十五》
下情没有不希望传达给君主的，上情没有不希图使臣下知晓的。但是，臣下总是苦于难以将下情传达到上面，君主总是苦于下面难知上情，为什么会这样呢？
下之情莫不愿达于上，上之情莫不求知于下，然而下恒苦上之难达，上恒苦下之难知。
The lower level does not want to communicate with the monarch, and the upper level does not want to make the ministers know. However, ministers always find it difficult to communicate with the upper level, and monarchs always find it difficult to know the lower level. Why is this so?