The army marched away. In the course of the march they passed through a wheat region, and the grain was ready for harvesting but the peasants had fled for fear, and the corn was uncut. Cao Cao sent proclamations to all villages and towns:

"I am sent on the expedition by command of the Emperor to capture a rebel and save the people. I cannot avoid moving in the harvest season; but if anyone trample down the corn, he shall be put to death. Military law is strict without exception, and the people need fear no damage."

The people were very pleased and lined the road, wishing success to the expedition. When the soldiers passed wheat fields, they dismounted and pushed aside the stalks so that none were trampled down.

One day, when Cao Cao was riding through the fields, a dove suddenly got up, startling the horse so that it swerved into the standing grain, and a large patch was trampled down. Cao Cao at once called the Provost Marshal and bade him decree the sentence for the crime of trampling down corn.

"How can I deal with your crime?" asked the Provost Marshal.

"I made the rule, and I have broken it. Can I otherwise satisfy public opinion?"

Cao Cao laid hold of the sword by his side and made to take his own life. All hastened to prevent him.

Guo Jia said, "In ancient days, the days of the Spring and Autumn history, the laws were not applied to those of the most important. You are the supreme leader of a mighty army and must not wound yourself."

Cao Cao pondered for a long time. At last he said, "Since there exists the reason just quoted, I may perhaps escape the death penalty."

Then with his sword he cut off his hair and threw it on the ground, saying, "I cut off the hair as touching the head."

Then he sent messengers to exhibit the hair throughout the whole army, saying, "The Prime Minister, having trodden down some corn, ought to have lost his head by the terms of the order; now here is his hair cut off as an attack on the head."

This deed was a stimulus to discipline all through the army so that not a person dared be disobedient.