This story is excerpted from the History of the Three Kingdoms.

In the late Han Dynasty, there were two talented writers named Zhang Hong and Chen Lin. Both had great esteem for each other's literary talents and works. Zhang Hong once wrote a letter to Chen Lin expressing his admiration for his literary grace. The other wrote in reply saying that compared to Zhang Hong, he was like a junior sorcerer in the presence of a great one. The original meaning was that a junior sorcerer cannot make his magic effective before a great sorcerer. Chen Lin used this to denote that his literary works were eclipsed by those by Zhang Hong.

Later, this phrase came to be used to denote that when two things are compared, one is obviously superior to the other.