一问三不知 — “Ask one, know nothing of three”

The idiom "一问三不知" (yī wèn sān bù zhī) originates from "Zuo Zhuan, Duke Ai's 27th Year." In 468 BCE, Gou Yao, a high official from the State of Jin, led a large army to attack the State of Zheng.

Zheng, once a powerful state, had weakened and sent its official, Gongzi Ban, to seek aid from the State of Qi. Duke Ping of Qi, wary of Jin's growing power, dispatched his official, Chen Chengzi, with troops to assist Zheng.

Upon reaching the Zishui River, heavy rain made the soldiers hesitant to cross. Zisi, Zheng's guide, urged haste, emphasizing Zheng's critical situation. Chen Chengzi, donning a rain cape, bravely commanded the army, even forcing frightened warhorses across the surging river. After successfully crossing, the Qi army prepared for battle.

Jin's commander, Gou Yao, observing the well-disciplined Qi forces, felt apprehensive. He remarked to his lieutenants that he had only divined for attacking Zheng, not for fighting Qi, and proposed a retreat. He then sent an envoy to Chen Chengzi, fabricating a story that Jin's campaign was meant to avenge Chen Chengzi's clan, which supposedly suffered due to Zheng. Chen Chengzi, infuriated by the blatant lie, retorted that oppressors never end well.

Later, a subordinate named Gou Yin reported to Chen Chengzi that someone from the Jin army claimed Jin planned a surprise attack with a thousand chariots. Chen Chengzi sternly rebuked Gou Yin, reminding him of their ruler's command not to fear large armies and declaring that such demoralizing words would be reported upon their return.

Realizing his blunder, Gou Yin regretfully said, "Today I understand why I am always distrusted and have to live in exile. A gentleman, when planning an affair, should consider its beginning, development, and outcome – these three aspects – before reporting. Now, I reported without knowing these three aspects. How could I not encounter difficulties?" A few days later, the Jin army retreated, and Chen Chengzi also led his army back to Qi. Gou Yin's regretful statement about not knowing the beginning, development, and outcome of a matter gave rise to this idiom.