Chen Gong
In 198, Cao Cao launched a campaign against his rival Lü Bu in Xu Province, leading to the Battle of Xiapi. Lü Bu lost three battles and retreated to Xiapi (下邳; present-day Pizhou, Jiangsu). Cao Cao's forces besieged the city for months but they still could not conquer it because Lü Bu and his men resisted firmly. By then, Cao Cao's troops were tired and weary of battle, so Cao intended to withdraw his forces. However, Guo Jia and Xun You told Cao Cao, "Lü Bu is courageous but foolhardy. His army's morale is low because he has already lost three battles. The troops look up to their commander. If their commander shows any sign of weakness, the men will lose their fighting spirit. Lü Bu may have Chen Gong as an intelligent adviser but the latter's strategies always come late. Now, we should take advantage of this situation, when the morale of Lü Bu's forces is low and when Chen Gong has yet to think of a solution, to press on a fierce attack and we'll achieve victory." Cao Cao heeded their advice and directed the waters of the Yi () and Si rivers to flood Xiapi, resulting in his triumph over Lü Bu.