Discourses: Book 3 16 : 1
The man who consorts frequently with one person or another either for conversation, or for banquets, or for social purposes in general, is compelled either to become like them himself, or else to bring them over to his own style of living; for if you put by the side of a live coal one that has gone out, either the dead coal will put the live one out, or the latter will kindle the former. Since the risk, then, is so great, we ought to enter cautiously into such social intercourse with the laymen, remembering that it is impossible for the man who brushes up against the person who is covered with soot to keep from getting some soot on himself. For what are you going to do if he talks about gladiators, or horses, or athletes, or, worse still, about people: "So-and-so is bad, So-and-so is good; this was well done, this ill"; or again, if he scoffs, or jeers, or shows an ugly disposition? Has any of you the capacity of the expert lyre-player when he takes up his lyre, which enables him, the instant he touches the strings, to recognize the ones which are off pitch, and to tune the instrument? Or the power that Socrates had, which enabled him in every kind of social intercourse to bring over to his own side those who were in his company? How could you have? But you must necessarily be converted by the laymen.