He who knows does not speak; He who speaks does not know. He who is truthful is not showy; He who is showy is not truthful. He who is virtuous does not dispute; He who disputes is not virtuous. He who is learned is not wise; He who is wise is not learned. Therefore the sage does not display his own merits.
Those who possess wisdom cannot just ladle it out to every wantwit and jackanapes who comes along and asks for it. A person must be prepared to receive wisdom, or else it will do him more harm than good. Moreover, a lout thrashing about in the clear waters of wisdom will dirty those waters for everyone else.