《汉书·传·董仲舒传》
可是普通的玉要是不雕刻，就不能成就美丽的花纹；君子不学习，就不能成就美德。
然则常玉不瑑，不成文章；君子不学，不成其德。
However, if ordinary jade is not engraved, it cannot achieve beautiful patterns; if a gentleman does not study, he cannot achieve virtue.