Two reasons, one is family, the other is grain and grass.
First, the influence of family members
When you go out to fight, your family members are in the rear.
Guan Yu's defeat was not defeated by the Cao army, but was copied by Eastern Wu, and Guan Yu's family and the soldiers' families were captured by the Eastern Wu army. Moreover, in order to demoralize Guan Yu's army, Lü Meng asked the families of these soldiers to write letters, and asked Guan Yu's emissaries to carry the letters to the army.
When the messenger came out of the village, all the generals came to inquire about the affairs of the house; the messenger said that the house was all right, and Lu Meng was extremely gracious, and transmitted the letter to the generals. Each will rejoice, but no one will fight.
Guan Yu sympathized with the soldiers and did not stop this matter at the first time. For an ordinary person, the family is the pillar, and many soldiers choose to secretly break away from Guan Yu's troops and flee back to Jingzhou for the sake of their families.
Zhao Yun had never faced such a situation as Guan Yu, even if he lost the battle, the soldier's family members were in the rear, it was safe, for the sake of the family, the soldiers had to fight desperately.
Of course, not all soldiers will be burdened by the family, no worries does not mean that they do not have any worries, they also have to face the second problem.
Second, the issue of grain and grass
As the saying goes, "People are iron rice is steel, and a meal is not eaten hungry and panicked."
Guan Yu launched the Battle of Xiangfan with the three counties of Jingzhou as the capital, and fought for a very long time (from the time of summer and autumn to the end of winter), and he received nearly 30,000 prisoners from Yu Ban in the early stage. The pressure on grain and grass was so great that the history books even recorded that Guan Yu robbed Eastern Wu of rice grains.
Guan Yu's army lacked food, which was also reflected in the interpretation. During the rendition, Jingzhou was attacked by a sneak attack, and Fu Shiren of the public security surrendered, and offered to persuade the Nan Commandery to guard the general Mi Fang. When Mi Fang hesitated, Guan Yu's emissaries came with military orders, which completely dispelled Mi Fang's hesitation.
Just as he was hesitating, he neglected to declare that the official dispatch was sent to the hall. The emissary said: "There is a shortage of grain in the Guan Gong army, so he took 100,000 stones of white rice from the South County and the Second Place of the Public Security Department, and ordered the Second General to go to the army at night to deliver it." Such as chi li chop. ”
In fact, even if Mi Fang re-bales straw, the matter of escorting grain and grass should not be slackened to this extent. The only explanation is that Jingzhou is extremely short of grain, and the grain and grass collected or collected are not enough to support the consumption of Guan Yu's army. That is to say, the grain and grass in Guan Yu's army should be running out soon.
The pressure on Mi Fang to collect military food should be very large, although Nan County is a big county, but after the war, the population is very poor, far less prosperous than Jingbei County. Now that the city is besieged by the Eastern Wu army, it is basically impossible to collect grain and grass in the counties outside the city.
Mi Fang chose to surrender, it is likely that there is no grain and grass in the city, at least the grain and grass in the city will not last long. Even if Guan Yu could return to the rescue in time, he might be defeated because of the grain and grass problem.
Later, Guan Yu returned to rescue Jingzhou, but there was no fierce battle with Eastern Wu, and finally retreated to Maicheng without any food. This shows that Guan Yu's army food and grass have become a problem.
Without food to eat, it is the fate of starvation. In this case, who will support ordinary soldiers except for their relatives? Guan Yu was also aware of his situation, and the soldiers did not take measures to stop them from escaping.
Zhao Yun was known as the "General of Constant Victory", and the number of defeats was actually very small. One was that Changshanpo was pursued by the Cao army, and the other was that during the Northern Expedition, he was caught by Xiahou Shu's strategy and was besieged by the Wei army.
The first time, there was actually no reference significance, Liu Bei's army was scattered, and there was no one around Zhao Yun. The second time was actually of little significance, and Zhao Yun was quickly released by Guan Xing and Zhang Bao after being trapped.
Soldiers cannot surrender as soon as they are trapped. What's that? So there is no grain and grass problem in it at all.
If there were no reinforcements, Zhao Yun would be besieged for ten days and eight days, and the situation would be different. Of course, Zhao Yun couldn't let such a thing happen, and without waiting for the grain and grass to be cut off, he would definitely break through with all his might.