fáng mín zhī kǒu, shèn yú fáng chuān 防民之口，甚于防川
To Silence the People Is More Harmful than Blocking a River.
Silencing the people and preventing them from expressing their opinions is more damaging than blocking the course of a river and causing a flood. Fang (防) means “a dike” to stop water flowing, and its extended meaning is to “block,” “prevent,” or “stop.” Obstructing the river flow will make the water rise and wash away the dikes, causing uncontrollable flooding. The ancients used this analogy to describe the serious harm that could occur if the public was not allowed to express its opinions. Taken from a positive angle, it means that the public will is powerful and irresistible, and that a ruler should allow its expression, or else expect popular resistance. The idea is in line with such expressions as that people are the foundation of the state, the people’s will is the foundation of the state, and people can float the boat (of state) or sink it.
The harm caused by not letting people express their opinions is greater than blocking a river. When a river breaks its banks many people are harmed. The same is true for blocking the expression of popular sentiment. That’s why those who manage rivers must clear away obstructions so the water flows smoothly; those who rule the people must remove impediments and encourage people to speak out their mind. (Discourses on Governance of the States)