Xun You was a renowned strategist during the Three Kingdoms period. When Dong Zhuo seized power and terrorized Chang'an, Xun You conspired with He Yong and Zheng Tai to assassinate him, but their plan was discovered before it could be executed, and they were arrested and imprisoned. He Yong, fearing Dong Zhuo's brutality, committed suicide, yet Xun You remained calm and composed, eating and conversing as usual. After Dong Zhuo's death, he was released and lingered in Jingzhou.
Cao Cao, always on the lookout for talent, had long heard of Xun You's brilliance. He wrote to him, "The world is in chaos—this is the perfect time for a strategist to shine. Yet you linger in Jingzhou, wasting your days?" When Xun You arrived, Cao Cao personally received him. After their conversation, Cao Cao turned to his attendants and said, "Xun You is no ordinary man. With him by my side to plan great affairs, what do I have to worry about?" He immediately appointed Xun You as his military advisor.
From that point on, Xun You remained by Cao Cao's side, offering strategic counsel at every turn.
In 198 AD, during the third year of the Jian'an era, Cao Cao besieged Lü Bu in a long campaign. Exhausted and ready to retreat, his advisor Xun You urged, "Lü Bu is brave but reckless; his defeats have drained his spirit. An army's morale follows its commander—if he falters, his troops lose heart. Strike now while they're gasping for breath, and we can crush them completely." Heeding this advice, Cao Cao pressed the attack, ultimately capturing and executing Lü Bu.
When Cao Cao lifted the siege at Baima, he used strategist Xun You's plan to slay Yuan Shao's general Yan Liang. As Cao Cao withdrew, Yuan Shao's forces pursued in overwhelming numbers, causing Cao's troops to panic and urge retreat to camp. Only Xun You said, "This is the perfect chance to lure the enemy!" Agreeing with Cao Cao, they abandoned supplies to tempt Yuan's army, who scrambled for the loot, throwing their formation into chaos. Seizing the moment, Cao Cao ordered a sudden cavalry and infantry assault, crushing Yuan Shao's forces.
After pacifying Yizhou, Cao Cao highly praised Xun You's repeated strategic counsel, once memorializing Emperor Xian Liu Xie: "Military advisor Xun You has assisted me since the founding of our enterprise, accompanying me on every campaign; every victory over the enemy was achieved through his plans." Xun You was enfeoffed as Marquis of Lingshu Pavilion with a fief of seven hundred households, and after the establishment of Wei, he served as Master of Writing.
Xun You was a brilliant strategist known for his sharp mind and careful planning, yet he never flaunted his talents or boasted of his achievements. He kept state secrets so tightly that no outsider ever learned of his military and political schemes. Whenever Cao Cao spoke of him, he praised, "Xun You appears dull on the outside but is wise within; he seems timid but is brave and resolute. He never brags about his strengths or shows off his merits. Others can match his intelligence, but they cannot match his wisdom that appears foolish." After Xun You's death, Cao Cao wept every time he mentioned him, grieving the loss of such an exceptional advisor.
Later, the idiom "Outwardly Foolish, Inwardly Wise" came to describe someone who appears dull on the outside but is intelligent within.
Source: *Records of the Three Kingdoms*, "Biography of Xun You"
Meaning of the Idiom: Later, the Chinese idiom "外愚内智" came to describe how someone appears dull on the outside but is intelligent within.