We can know a person by observing his behaviour, understanding the reasons for his actions and ascertaining his intentions. If we do this, how can we not know him?
When a person should be spoken with, and you don't speak with them, you lose them. When a person shouldn't be spoken with and you speak to them, you waste your breath. The wise do not lose people, nor do they waste their breath.
Earnest in practicing the ordinary virtues, and careful in speaking about them, if, in his practice, he has anything defective, the superior man dares not but exert himself; and if, in his words, he has any excess, he dares not allow himself such license.