This is an old saying, the original words are: "With copper as a mirror, you can dress your clothes;" Taking history as a mirror, we can know the rise and fall; Taking people as a mirror can distinguish right from wrong ... "Translated into modern Chinese: looking at yourself with a mirror (ancient bronze mirror) can correct your clothes and accessories; Based on historical experience and lessons, we can understand the reasons for the rise and fall of dynasties; By learning from other people's experiences and lessons, we can know whether our manners and behaviors are right or wrong (right or wrong).
Note: The word "Jian" in the sentence originally meant ancient bronze mirror, and extended to the meaning of comparison and reference.