Analects 2:22 makes the case for trustworthiness with an image from the roads. I do not know, Confucius says, how a person without xin is to get on. How can a large carriage be made to go without the crossbar pin, or a small carriage without the yoke pin? The pins in question are small components, wooden or bronze, that join the yoke to the shaft: nearly invisible in the assembled vehicle, of negligible cost beside the lacquered body and the matched horses, and absolutely indispensable, because without them the carriage and its motive power are simply two objects standing near each other. The analogy is precise. A person's capacities, talent, learning, strength, wealth, are the carriage; society's cooperative life is the journey; and xin, the reliability of one's word, is the pin by which the one is hitched to the other. Break it and nothing else functions, however splendid. The character for xin is itself a compact argument, joining the graph for person to the graph for speech: trustworthiness is a person standing by their words.
The Analects returns to the theme constantly: Zengzi examines himself daily on whether he has kept faith with friends; a state, Confucius says, can survive the loss of arms and even of food, but not the loss of the people's trust, for without trust there is no standing at all. In the Confucian accounting, xin is not one social grace among many; it is the fastening on which every relationship, commercial, political and personal, actually hangs.