In the early Spring and Autumn period, the State of Zheng grew powerful under Duke Zhuang of Zheng, who planned to annex neighboring states and dominate the Central Plains. Knowing that Qi was large but weak and could be used for now, he first befriended the strong State of Lu, then formed a three-state alliance with Qi, creating a horizontal political force from west to east to jointly deal with smaller states before pursuing his own hegemony.
The Duke of Qi, seeking to strengthen his alliance with the state of Zheng, sent a special envoy to propose a marriage between his daughter Wen Jiang and Prince Hu, the crown prince of Zheng. At that time, Hu, the son of Duke Zhuang of Zheng, had grown into a handsome and capable young man. Years earlier, at just sixteen or seventeen, he had served as a hostage in the Zhou capital Luoyang during the "Zhou-Zheng hostage exchange." Later, his father had him study military strategy, and he became a competent commander. Duke Zhuang was immensely proud of him and had named him heir. Now, the unexpected marriage proposal from Qi arrived. After a moment's thought, Duke Zhuang told the Qi envoy, "This matter must be decided by my son himself."
Prince Hu suddenly, without thinking, flatly refused: "Each person should have a suitable spouse; marriage should be well-matched. Qi is a great state, and a daughter of a great state is not one I dare to marry. Please convey this reply to the king."
Later, Duke Zhuang of Zheng asked why he had rejected the marriage proposal. Crown Prince Hu replied, "A gentleman once said that one should be good at planning for oneself. How could I trouble my father over my own marriage? If this marriage went through, I might end up being controlled by the state of Qi."
Duke Zhuang of Zheng nodded and sighed, "Truly my son."
Soon after, the northern Shanrong tribe attacked Qi, which was too weak to defend itself and had to seek help from Zheng. Duke Zhuang of Zheng sent Crown Prince Hu to lead the army to Qi's aid. Prince Hu commanded with calm authority, and the well-trained Zheng troops, though facing the fierce but tactically unsophisticated Shanrong warriors, ultimately defeated them. Prince Hu crushed the Rong forces, pursued them in victory, captured two enemy generals and three hundred armored soldiers, and handed all the prisoners over to Qi.
The Duke of Qi, impressed by Crown Prince Hu's victory over the Rong army, grew even fonder of him and personally offered his daughter Wen Jiang in marriage. Yet Crown Prince Hu firmly declined again, leaving the Duke quite displeased.
Later, someone asked Crown Prince Hu why he refused the marriage. He replied, "When I had done nothing for the State of Qi, I still dared not marry their princess. Now that I have come to rescue Qi from crisis, if I accept the proposal, won't people back in Zheng think I only led my troops here to gain a favor from Qi? How could I allow such a misunderstanding?"
Crown Prince Hu's careful self-preservation had its own logic—by twice refusing marriage alliances, he skillfully avoided political entanglements, a perfectly sound strategy.
"In the idiom 'Skillful in Self-Planning,' 'skillful' means adeptly, and 'planning' means strategizing. It refers to being good at planning for oneself."
Source: *Zuo Zhuan*, Chapter "Duke Huan's Sixth Year"
Meaning of the Idiom: Later, the Chinese idiom "善自为谋" came to describe being good at planning for oneself.