Discourses, "That We Ought with Caution to Enter Into Familiar Intercourse with Men" (§1)

“If a man has frequent intercourse with others either for talk, or drinking together, or generally for social purposes, he must either become like them, or change them to his own fashion. For if a man places a piece of quenched charcoal close to a piece that is burning, either the quenched charcoal will quench the other, or the burning charcoal will light that which is quenched.”