Proficiency in a particular line

Gong sun Long , is a famous scholar lived in the State of Zhao during the Warring States Period (475-221BC). He had kept a circle skilled people around him. He often said, "A wise man should welcome anyone with a specialty."

One day, a man dressed in tattered and dirty clothes came to see him and said to him:" I have a special skill."
Gong asked: "What is it?"
"I have a loud voice and I'm good at shouting."
Then Gong turned to his followers and asked, " Who is good at shouting?" But none of them answered "Yes". So the scholar took the man in.

Some days later, Gong and his followers went on a trip. They came to a wide river and found the ferryboat was on the other side of the river. All of them had no idea. Suddenly, Gong thought of the shouting expert and turned to him, "Can you have a try?" The man realized it was the chance to show his skill. He shouted to the ferryman as loud as he could, "Hey, ferryman, come here, we want to cross the river." As his voice ended, the ferryman came to fetch them. Gong was very satisfied with the new follower.

Later, people use it to describe anyone who has a special professional skill.

一技之長

戰國時期，趙國有位名士叫公孫龍。他手下聚集了許多有自己特長的門客。他常說：「一個聰明人應該善於接納每一個有自己特長的人。」

一天，有一個穿著很破爛的人來見他，並向他推薦自己：「我有一項特別的本領。」公孫龍就問道：「什麼本領？」那個人回答道：「我聲音特別大，很善於叫喊。」公孫龍聽了，就轉身問他旁邊的門客：「你們有誰善於叫喊？」結果沒有一個人回答「是」。於是，他就收下了這個很善於叫的人作他的隨從。

沒過多久，公孫龍和他的門客一起出外遊玩。他們來到一條很寬的河邊，發現渡船在河的另一頭，所有人都不知怎麼辦好。突然，公孫龍想起他最近收的那個人的本領是善於叫，於是，他就轉過頭去對那人說：「你大聲叫對面的船夫，看能不能把他叫過來。」那人覺得展示他技能的時候到了，就盡力大聲向對面喊：「喂，船夫，過來，我們要過河。」當他叫聲剛完，那對面的船夫就搖著船過來了。公孫龍對這個新收的門客非常滿意。

後來，「一技之長」就用來形容一個人有一項特殊的本領。