There was a man whose only son died of a sudden illness. He did not mourn for his son, nor was he sad about it. His friends were curious about his behaviour, so they asked him, “Your only son is dead. You should be heartbroken. Why do you act as if nothing had happened?” The man replied, “Before my son came, I had no son. I was certainly not heartbroken back then. Now I have no son. Why should I be heartbroken now?”

(The Liezi)