《论衡·卷十·非韩篇》
坏人一定要等自己的耳朵听到，眼睛看到之后才知道，那么郑国查出来的坏人就太少了。
奸必待耳目之所及而後知之，则郑国之得奸寡矣。
Bad people must wait for their ears to hear it and their eyes to see it before they know, so there are too few bad people found out in the state of Zheng.