Yan Zi of the state of Qi was sent on a diplomatic mission to the State of Chu.
One day, the King of Chu held a banquet in Yan Zi's honor. While they were feasting, two minor officials escorted a prisoner before the king.
Deliberately, the King of Chu asked, "What crime has this man committed?"
One official replied, "He is a robber."
The King of Chu asked again, "Where is he from?"
The official answered, "He is from the State of Qi."
The King of Chu turned to Yan Zi and said, "So the people of Qi are accustomed to robbery."
Yan Zi stood up and replied, "Your Majesty, I have heard that when orange trees from south of the Huai River are transplanted north of it, they become trifoliate orange trees. Outwardly, their leaves look alike, but the taste of their fruits is entirely different. The people of Qi never commit robbery in their homeland, but once they come to the State of Chu, they start engaging in crime. Perhaps this is due to the influence of the local environment and customs here."
Hearing this, the King of Chu was struck dumb with shame.