To "take the mirror as a mirror, you can be well dressed; Take people as a mirror, you can know the gains and losses; Only by taking history as a mirror can we know why.
This is how Emperor Taizong felt after the death of Wei Zhi, the remonstrator. The core is the last two sentences. Paying attention to talents and being good at learning from history will help the monarch to understand the right and wrong of his own administration and consolidate his political power. (Attachment: "Taking history as a mirror, we can know the replacement" should be "Taking history as a mirror, we can know the replacement")