Sun Gan, the word Gong You. I am a graduate student at Zheng Xuan, a famous professor in Han Dynasty. After Liu Bei became a shepherd in Xuzhou, he was hired as an official. In the Han Dynasty, there were two people who worked for Zhou Mu, ranking second only to Zhou Mu: one was engaged in managing China, and the other was engaged in driving. Manage China's internal affairs, not diplomacy. It can be inferred from the fact that Sun Gan went to see Yuan Shao and Liu Biao several times later that he was engaged in other driving work. In Romance of the Three Kingdoms, Sun Gan was recommended to Liu Bei by Tao Qian before he died: Old Tao Qian knew that his death was coming, and wanted to give Liu Bei the post of shepherd in Xuzhou. Seeing that Tao Qian was running out of breath, Liu Bei said half-heartedly, "I can't bear such a big thing alone." Tao Qian, kind and honest, said, "I recommend someone to help you. This man is from Beihai. His surname is Sun and his name is Gan. Suitable for this job. " Discovery problem: Sun Gan could not have been discovered by Tao Qian when he was dying. Why not use it earlier, but wait until you die before recommending it to Liu Bei? According to the biography of the reflection of Sun Gan and its annotations, we can roughly infer that the real situation in history is this: after Liu Bei became a herdsman in Xuzhou, Sun Gan, a graduate student of Professor Zheng Xuan, wanted to go into politics, while Zheng Xuan was a famous professor and was very happy politically. Moreover, Zheng Xuan's other disciples Lu Zhi is Liu Bei's mentor, so it is easy to recommend his beloved disciple to Liu Bei.