In order to attack Liu Bei, Yuan Shu invited Lü Bu to join forces and promised to provide Lü Bu with money and food. However, when Lü Bu sent troops, Yuan Shu tricked Lai into not giving money and grain, which made Lü Bu very angry. The second time Yuan Shu invited Lü Bu to send troops again, and first gave Lü Bu a million catties of grain, according to the reason, Lü Bu had already received money and grain this time, and should take the initiative to send troops. However, this time Lü Bu did not send troops, and his attitude towards Yuan Shu changed from enthusiasm to indifference. Why did Lü Bu's attitude change so much before and after? There are two reasons for this.
First, Lü Bu received letters from Liu Bei.
Liu Bei told Lü Bu: "General Fu Zi is hanging on to his thoughts, and orders Xiao Pei to be present, and he really worships the virtue of the clouds and heavens." Now Yuan Shu wanted to avenge his personal revenge and sent Ji Ling to lead the troops to the county. Death is imminent, and no general can save it. I hope to drive the division of the first brigade to save the overhanging urgency, and I am very fortunate!" The information liu bei emphasized in the letter was mainly Lü Bu's kindness to Liu Bei. Liu Bei said that instead of thinking about Lü Bu's seizure of Xuzhou, he was grateful to Lü Bu for taking him in Xiaopei. Then he asked Lü Bu to send troops to rescue him. It can be said that Liu Bei's letters only emphasize his gratitude, and for Lü Bu, the persuasiveness is not strong. It is your business that Liu Bei was attacked by Yuan Shu, and what does it have to do with Lü Bu?
Second, Lü Bu's own judgment of the situation.
This is the most critical point. After receiving Liu Bei's letter, Lü Bu and Chen Gong analyzed the situation: "The former Yuan Shu sent grain to the letter, and Gai wanted me not to save Xuan Deye. Now Xuande came again for help. I want Xuan Detun Army Xiao Pei, may not be able to harm me; If Yuan Shu merges with Xuande, then the Northern Taishan Generals will try to figure me out, and I can't rest on my laurels. It is better to save Xuande. It is clearly stated in the speech that this passage is not Chen Gong's preaching, but from Lü Bu's own judgment -- this is also in line with the records in the canonical history. Lü Bu saw yuan shu and Liu Bei's interests very clearly. Once Yuan Shu eliminated Liu Bei, then Yuan Shu could use Xiao Pei to occupy the prefectures and counties outside pengcheng, thus isolating Pengcheng and occupying the entire Xuzhou.
It can be said that Lü Bu's vision is still very sharp, and he also looks at the problem very long-term. Then, why didn't Liu Bei tell Lü Bu about these stakes? I think there are two reasons. On the one hand, there is no record of Liu Bei's letters in the main history, and on the other hand, Luo Guanzhong strives to highlight Liu Bei's image of benevolence. Even if Lü Bu was not kind at the beginning, Liu Bei did not complain at all, but was grateful to Lü Bu.