Source: "Old Tang Book Wei Zhi Biography" Li Shimin: Fu can dress with copper as a mirror; Taking history as a mirror, we can know the rise and fall; Take people as a mirror, you can know the gains and losses.
With copper as a mirror, clothes can be straightened, that is to say, people's clothes and hats can be found with a copper left mirror (used in ancient times), that is to say, people's external image can be seen.
Taking people as a mirror, we can know the gains and losses, that is, we can learn from people's things and know what we should do, what we get and what we lose in everything we do.
Taking history as a mirror, we can know the rise and fall, that is to say, taking history as a mirror, we can know the rise and fall of a country.
Extended data
This sentence was said by Li Shimin, the prime minister of Emperor Taizong. Wei Zhi died, and Emperor Taizong cried very sadly. He said: I have three mirrors (they used to be bronze mirrors). "With copper as a mirror, I can dress." I can put on his clothes and hat.
"Taking history as a mirror", observing his own administration with history, "knowing the rise and fall", how to make the dynasty prosperous and how to make the dynasty perish, he can observe from history;
"Taking the people as a mirror" requires a wise minister to convince him to "know the gains and losses", so that you can understand the gains and losses of all his policies and then correct them.
Emperor Taizong said that he had these three mirrors. When Wei Zhi died, one side was broken.