Laozi once went to visit the sick sage Shang Rong, and consulted him with some philosophical problems.

Shang Rong told him that when he passed his hometown he should get off the chariot. Laozi asked, "Is this meant to show that I have not forget about the people in the hometown?"

Shang Rong nodded and added that when he passed an old tall tree he should walk fast in small paces. Laozi said, "Do you mean we should respect seniors?"

Shang Rong nodded again, and opened his mouth and asked, "Is my tongue still there?" "Yes", Laizi repled. "Is my tongue still there?" "No," Laozi answered, "Do you know what this mean?" Shang Rong said. Laozi answered, "You are telling me that the teeth fell off early because of their hardness while the tongue lasts long because of its softness?""Exactly! You already know all priciples and truths in the world."

老子去探望病重的哲人商容，并请教有关的哲学问题。

商容告诉他在经过故乡时要下车，老子问道：“这是不是表示不忘记故乡的人？”

商容点点头，又说经过高大的老树要小步快走，老子回答说：“你的意思是说一定要尊敬老人？”

商容又点点头，然后张开口问道：“我的舌头还在吗?”老子说：“在”。商容又问：“我的牙齿还有吗？”老子说：“没有了。”商容说：“你知道这是什么意思吗？”老子说：“先生想告诉我牙齿因为刚硬而过早夭亡，舌头因柔软而长久存在这个道理吗？”商容说：“对！你已经明白天下的事理。”