During the reign of Emperor Xianzong of the Tang Dynasty, Zhang Hongjing served as Vice Director of the Secretariat and was later promoted to Minister of Personnel, then appointed as Military Governor of Xuanwu Army, before replacing Liu Zong as Military Governor of Youzhou.
Zhang Hongjing came from a family of officials but knew nothing of local customs. His career had been a smooth ascent, and he was rather proud of it. When he arrived in Youzhou, he flaunted his power along the way, his carriage so lavish and ornate that it stood out among the troops. The common folk who saw him felt a chill of fear, wondering, "With such a grand carriage and such extravagant luxury, can he possibly do any good for us?" The local officials, too, were terrified of this overbearing superior.
Upon taking office, Zhang Hongjing's first act was to dig up An Lushan's grave and destroy his coffin. He believed that since An Lushan's rebellion had started in Youzhou, reforming local customs must begin here. The local people, seeing him exhume a man who had been dead for decades, only grew more disillusioned with him.
Zhang Hongjing was a lax military governor. Two of his subordinates, Wei Yong and Zhang Zonghou, often gathered a group to drink at a tavern until midnight, stumbling back drunk. They ordered soldiers to light lanterns and torches to escort them home, making a racket through the streets that infuriated the locals. The pair treated soldiers harshly, cursing them as "rebel slaves" at the slightest provocation. They once sneered, "In these peaceful times, being able to draw a two-stone bow is worthless—better to recognize the character 'ding'." The soldiers seethed with hatred.
When Liu Zong, the former military governor of Youzhou, sent one million strings of cash to reward the troops, Zhang Hongjing secretly pocketed two hundred thousand for his own administrative expenses, distributing only eight hundred thousand to the soldiers. The troops, already seething with resentment against Wei Yong and Zhang Zonghou, erupted in fury. They rose up together, killed Wei Yong and Zhang Zonghou, seized Zhang Hongjing, and imprisoned him at Jimen Hall. The soldiers then declared Zhu Hui their leader, igniting a full-scale rebellion.
Zhang Hongjing was demoted to governor of Fuzhou for this incident, and though he served only briefly as military commissioner of Youzhou, his infamy spread far and wide.
The character "ding" is the easiest to recognize, yet one cannot even identify it—hence the idiom "cannot recognize the character 'ding'" describes someone who is completely illiterate.
Source: *Old Book of Tang*, "Biography of Zhang Hongjing"
Meaning of the Idiom: Later, the Chinese idiom "目不识丁" came to describe how one cannot even identify the character "ding" describes someone who is completely illiterate.