Digging the wall and stealing light are idioms and allusions. It describes the story that Kuang Heng studied hard in the Western Han Dynasty and eventually became a great scholar. Nowadays, people generally use this idiom to describe diligent study and hard study.

1. Kuang Heng studied hard without a candle. His neighbor had a candle but didn't catch it. Heng Nai led his light through the wall and read a book reflecting the light. City people can't read their surnames. They have money at home and many books. Therefore, Heng is cooperating with him, not claiming compensation. The master asked Heng strangely, and Heng said, "May the master read all the books." The host sighed, gave books and became a university. (Selected from Xin's Miscellanies of Xijing, Volume II)

2. Kuang Heng is eager to study without candles; Neighbors have candles, but not enough. Constant reading by the light reflected from the cave wall. There are literati in the city, rich at home and many books. Hengnai helps them work for free. The master asked him strangely and said, "I wish I could get the master's book to read." The master feels his words, writes in words and becomes a university.