Cao Cao killed a lot of people, but there were many times when Cao Cao killed people that made people very confused. He killed some people who clearly shouldn't have been killed; he killed some people who clearly shouldn't have been killed, but Cao Cao killed them.

has an example, which is to kill the fire fighter.
In his later years, Cao Cao often stayed in Yecheng, and Xu Du's large and small affairs were left to the Prime Minister's Office, Shi Wang Bi. Shi, the chief minister of the Prime Minister's Office, is somewhat similar to today's secretary-general. He was able to hand over Xu Du to Wang Bi, which shows that Wang Bi has won Cao Cao's trust.
Because Cao Cao himself was not in Xudu, Shaofu Geng Ji, Prime Minister Sizhi Wei Huang, Imperial Physician Ling Jiben and others launched a rebellion, hoping to seize the opportunity to seize Xudu and Emperor Xian of Han . The rebels led more than a thousand people, including miscellaneous people and household children, to burn the door on fire and attack Wang Bi at night. Wang Bi was hit by an arrow and died a few days later.
When Cao Cao learned that the king would die, he was furious. He summoned all the officials in Xudu to Yecheng and asked those who put out the fire to stand on the left and those who did not put out the fire on the right. Everyone thought that those who put out the fire would be innocent, and most of them stood on the left. However, Cao Cao made a shocking decision, saying "Those who do not put out the fire are not contributing to the chaos, and putting out the fire is a real thief" and killed all the officials standing on the left.
This action of Cao Cao is incredible. The fire-fighter is actually a bandit.
Actually, this is easy to understand. When the rebels besieged Wang Bi in the prime minister's palace, how could anyone put out the fire in such a large-scale rebellion? Either they are afraid to stay at home, or they are going to put down the rebellion, but they will never put out the fire, so those who put out the fire are actually rebels.
Looking at it this way, although Cao Cao's killing was cruel, it was not completely unreasonable.
In the case of Wang Bi, Cao Cao's killing was too heavy, but some people looked like they were going to be killed, but Cao Cao did not kill them.
The first one is Wei Zhong.
When Cao Cao attacked Xuzhou Tao Qian, Lu Bu took Yanzhou 's nest from behind. Many city defenders saw that the situation was not good and surrendered to Lu Bu. Only three cities were still in Cao Cao's hands. After hearing this, Cao Cao said: Only Wei Zhong would not betray me.
didn't know that he would be slapped in the face soon, and Wei Zhong also defected. Cao Cao was furious and vowed to kill Wei Zhong. Later, Cao Cao put down the rebellion and captured Wei Zhong alive, but did not kill him. Instead, he appointed him as the governor of Hanoi.
There is another person, named Bi Chen , who is Cao Cao's Biejia. The so-called Biejia is a bit similar to today's Secretary-General. Because of his relatively high status, he rides alone in a carriage when traveling, so he is called "Biejia".
When Lu Bu attacked Yanzhou, Bi Chen's parents were also captured by Lu Bu. Cao Cao called Bi Chen to him and said, "Go to your parents." When Bi Chen heard this, he immediately knelt down and kowtowed vigorously, showing that he had no second thoughts. This moved Cao Cao so much that he burst into tears and was deeply relieved.
Little did he know that Bi Chen was completely a performing artist. As soon as he left the door, he ran to Lu Bu. Cao Cao was not only teased, but his tears were also shed in vain.
After Cao Cao put down the rebellion, Bi Chen was also captured. Just when everyone was worried about him, Cao Cao unexpectedly released Bi Chen. The reason given by Cao Cao was that Bi Chen was a filial son, and such a person was also loyal and reliable.

Cao Cao killed many people, and the one who should not be killed was definitely Hua Tuo.
Cao Cao suffered from a headache, so he asked Hua Tuo to treat him. After examination, Hua Tuo told Cao Cao that there was no way to cure the disease, and he could only slowly nurse it back to health. With Hua Tuo's help, Cao Cao's headache also improved somewhat.
But Hua Tuo was a famous doctor after all, and he was unwilling to stay with Cao Cao for a long time, so he lied that his wife was sick and needed him to go home to take care of her. Cao Cao also agreed to this request.
After Hua Tuo left, Cao Cao's headaches recurred. Cao Cao asked Hua Tuo to come back to see him. Several times in a row, Hua Tuo never came. Cao Cao sent someone to see if Hua Tuo's wife was really sick, and Hua Tuo's lie was exposed. Cao Cao was naturally very angry and killed Hua Tuo. Xunyu certainly knew the importance of Hua Tuo, so he advised Cao Cao. Cao Cao did not listen to the advice and killed Hua Tuo.
Hua Tuo's death will not do any good to Cao Cao. Hua Tuo's death also meant that Cao Cao's life had entered a countdown, and his head disease eventually killed him.

Postscript
Cao Cao killed countless people throughout his life. He also had large-scale massacres and pardoned some people who should have been sentenced to death. Cao Cao sometimes feels inexplicable when he kills people, and sometimes he is the one who must be killed, but Cao Cao generously lets him live.
This is Cao Cao's killing rule.