Nothing is clear and they rely on the most uncertain guide—common opinion

From The Daily Stoic by Ryan Holiday and Stephen Hanselman. 

Tranquility can’t be grasped except by those who have reached an unwavering and firm power of judgment—the rest constantly fall and rise in their decisions, wavering in a state of alternately rejecting and accepting things. What is the cause of this back and forth? It’s because nothing is clear and they rely on the most uncertain guide—common opinion.

—SENECA, MORAL LETTERS, 95.57b–58a