During the Warring States period, there was a master of the zhu, a stringed instrument, named Gao Jianli. He was a close friend of Jing Ke, and the two often drank and sang together.
Soon after, Crown Prince Dan of Yan personally requested Jing Ke to assassinate the King of Qin, and Jing Ke agreed. As he prepared to depart, Prince Dan saw him off in person, joined by Jing Ke's close friend Gao Jianli and several others.
At the Yishui River on the border of Yan, Gao Jianli struck the zhu while Jing Ke sang the heroic and solemn verse, "The wind rustles, the Yishui chills; the brave man leaves, never to return," then departed with tears.
But Jing Ke's assassination attempt on the First Emperor of Qin ultimately failed, costing Jing Ke his life. The enraged emperor ordered a manhunt for Crown Prince Dan of Yan and Jing Ke's associates. Gao Jianli was forced to change his name, flee to a remote village, and work as a hired laborer. The grueling labor wore on him, and as time passed, he grew increasingly bitter and restless.
During a banquet hosted by his patron, a guest performed on the zhu, an ancient stringed instrument. Gao Jianli, unable to contain his musical passion, began critiquing the performance, pointing out which passages were masterfully played and which fell short.
When the host learned of this, he asked Gao Jianli to perform for the guests. His extraordinary skill left everyone in awe. Gao Jianli also revealed his identity, then brought out his beloved zither from a long-hidden chest and changed back into his former attire. The crowd was both astonished and delighted; the host no longer treated him as a servant but honored him as a distinguished guest.
Later, people used the idiom "itch to show one's skill" to describe someone with talent who can't resist showing off when the opportunity arises.
Source: Ying Shao (Han Dynasty), *Comprehensive Meaning of Customs and Practices*, Chapter "Sounds"
Meaning of the Idiom: Later, the Chinese idiom "技痒难忍" came to describe how someone with talent can't resist showing off when the opportunity arises.