Shen Pei
In 200, when the Battle of Guandu broke out between Yuan Shao and Cao Cao, Xu You advised Yuan Shao to adopt a slow, steady and step-by-step approach towards attacking Cao Cao, but Yuan Shao again refused to listen as he preferred an all-out approach. Xu You, who was notorious for being greedy and corrupt, had allowed his family members to solicit bribes and commit crimes. Shen Pei, another of Yuan Shao's subordinates who was in charge of coordinating the mobilisation of troops for the Guandu campaign, had Xu You's family members arrested. Shen Pei then reported it to Yuan Shao, who scolded Xu You. Xu You, fearing that he had fallen out of Yuan Shao's favour, escaped from Yuan Shao's camp and defected to Cao Cao's side. Cao Cao was so overjoyed when he heard of his old friend's arrival that he even forgot to wear his shoes when he came out to welcome Xu You. Xu You pointed out the location of Yuan Shao's supply depot at Wuchao (烏巢) and urged Cao Cao to attack Wuchao and destroy Yuan Shao's supplies to force the enemy to retreat. During the battle Xu You advocated the execution of Yuan Shao's soldiers. Cao Cao led a successful raid on Wuchao and destroyed all of Yuan Shao's supplies, leading to his eventual victory over Yuan Shao at the Battle of Guandu.