During the Spring and Autumn and Warring States periods, a man from Yingdu in the state of Chu was writing a letter to the prime minister of the state of Yan.
As dusk fell and the room grew dim, the letter writer called to his servant, "Raise the candle!"—meaning to have the candle lifted higher—but absentmindedly scribbled the words "Raise the candle" into the letter itself. When the Prime Minister of Yan received the letter and spotted those two words, he frowned in puzzlement, finding them completely out of place with the rest of the text.
After much deliberation and careful analysis, he finally grasped the meaning and explained to himself, "Holding up a candle means advocating brightness; advocating brightness means selecting and appointing virtuous talents. Only then can the state be governed better. That's it! This must be the meaning!"
The next day, he reported this matter and his own interpretation to the King of Yan. The king was very pleased and acted on the meaning of "hold a candle," selecting some virtuous talents. As a result, the state was governed very well.
Later, people used the idiom "Ying's Letter, Yan's Interpretation" to describe far-fetched analogies and twisting the original meaning.
Source: *Han Feizi*, Chapter "Outer Congeries of Sayings, Upper Left"
Meaning of the Idiom: Later, the Chinese idiom "郢书燕说" came to describe far-fetched analogies and twisting the original meaning.