西汉中后期，东海郡承县有一个农家孩子，名叫匡衡，字稚圭。他家世代种田，生活贫苦，可匡衡从小就好学。
In the middle and later Western Han, a farmer’s child named Kuang Heng, courtesy name Zhigui, lived in Cheng County in Donghai Commandery. His family had farmed for generations and was poor, but Kuang Heng loved learning from childhood.
当时书籍靠手抄，价钱不低。匡衡白天给人做雇工，挣来的钱几乎都用来买书；有时买不起，就借来抄写。
Books were copied by hand in those days and were not cheap. Kuang Heng hired himself out as a labourer by day, and spent almost everything he earned on books; when he could not afford one, he borrowed it and copied it.
《西京杂记》里说，匡衡“勤学而无烛”，邻居家有蜡烛，光却照不到他家。于是他就在墙上凿了一个洞，把书凑近洞口，借着透进来的光读书。
The Miscellaneous Records of the Western Capital say that Kuang Heng “was diligent in study but had no candle”, and that although a neighbour had one, its light did not reach his house. So he bored a hole in the wall, held his book close to it, and read by the light that came through.
为了能读到更多的书，他还到县里一户藏书很多的人家去做工，却不要工钱。主人觉得奇怪，问他想要什么，他回答：“只希望能把您家的书都读一遍。”主人很感动，就把书借给了他。
To gain access to more books, he went to work for a wealthy household in the county that owned a large collection, and asked for no wages. The master found this strange and asked what he wanted. “Only to read all the books in your house,” Kuang Heng replied. Moved, the master lent them to him.
就这样，他白天做工，夜里读书，把主人家的书读了个遍，学问大有长进，尤其精通《诗经》，后来成为当时有名的经学家。
So it went: by day he laboured, by night he read, until he had worked through his employer’s whole collection. His learning grew greatly; he became especially accomplished in the Book of Odes and was later counted among the noted classical scholars of his day.
匡衡的才学得到了朝廷的赏识，他先做官，又给太子讲经。汉元帝即位后，他一路升迁，最终在建昭三年当上了丞相，被封为乐安侯。
His talents won the court’s recognition. He took office, then lectured on the classics to the crown prince; after Emperor Yuan of Han came to the throne, he rose steadily and in the third year of Jianzhao became Chancellor, enfeoffed as Marquis of Le’an.
不过，史书里的匡衡并不是完人。汉成帝时，他因封地多占了四百顷田，被人告发“专地盗土”，被免去官职，回到家乡，不久去世。
The Kuang Heng of the histories was no flawless sage, however. Under Emperor Cheng he was accused of “monopolising land and stealing soil” because his estate had taken four hundred qing more than it should, was stripped of office, returned home, and died soon afterward.
“凿壁偷光”流传下来，讲的是他在贫苦中坚持读书的那一面。后来人们用它鼓励孩子：条件再差，也不要放弃学习。
What the idiom 凿壁偷光 preserves is the other side of him — persistence in study despite poverty. Later generations used it to encourage children: however poor the conditions, never give up on learning.