There was an unwritten rule in the Song Dynasty "Don't kill scholar-officials". Although it is not written in the law, it is more authoritative than the law, and the literati have raised it to the point of "ancestral law". According to the History of Song Dynasty, Song Taizu set up an oath tablet in the ancestral temple, which read "Don't kill scholar-officials and writers".

The status of scholar-officials in Song Dynasty is extremely high, and it is worthy of the name to say that Song Dynasty is a "dream paradise" for scholar-officials. There were many preferential treatments for literati in Song Dynasty, such as extremely generous salary and high social status.

During the period of Song Shenzong, Shaanxi was defeated in the war, and the emperor ordered the killing of a Cao official. However, Prime Minister Cai did object. He said: "Scholars have not been killed since our ancestors, and I don't want to start with your majesty."

Song Shenzong pondered for a long time and said, "It can match the thorn noodles." But Zhang Dun, the assistant minister under the door, objected: "If you do this, you will not kill it." Song Shenzong was puzzled, and Zhang Dun said, "A scholar can be killed but not humiliated." Song Shenzong was naturally furious. His expression and manner said, "I'm glad I can't do anything!" However, Zhang Dun did not give in at all. He said bluntly, "I wish I were so happy not to do it."

"Not killing literati" is actually the result of the emperor's compromise with the literati class. After the Song Dynasty was established in Zhao Kuangyin, Wushu was suppressed by words and the imperial examination was opened. As a result, the Song Dynasty eliminated the military chaos since the Five Dynasties, but the civil service group became the same as the emperor.

In the Song Dynasty, the power of the civilian class expanded unprecedentedly, while the imperial power declined rapidly. When Song Taizu was a civil servant, he dared not disrespect him. However, when he was in Song Shenzong, civil servants dared to accuse the emperor in the hall without mercy. Eating midnight snack in Song Renzong is sometimes criticized by civil servants, and the emperor has become a half puppet of the literati. In this case, the emperor naturally did not dare to kill the literati, otherwise he would lose the support of the greatest power in the DPRK.