Zeng Zi was one of Confucius's disciples.
One day, Zeng Zi's wife was going to the market. Their son wanted to go with her and threw a tantrum, crying and fussing nonstop. Unable to calm him, his wife bent down and said to humor him: "Go home now, my dear. Mama will be back soon. When I return, I'll kill the pig to make you a meal."
Hearing this, the son went home happily.
Shortly after, the wife returned. Zeng Zi tied up their fat pig, took out a sharp knife, and prepared to slaughter it. Seeing this, his wife hurriedly grabbed his hand and said, "What are you doing? I was only trying to humor the child."
Zeng Zi replied seriously, "How can you deceive a child? A child is young and does not understand the world; he learns by following his parents' example. If you deceive him now, he will learn to deceive others. Furthermore, if a mother deceives her child, the child will lose trust in her. How then can you educate him properly?"
With that, Zeng Zi raised his knife and killed the pig.