惩前毖后

lit. to punish a little to prevent a lot (idiom); to criticize former mistakes firmly to prevent large scale repetition

to learn a lesson from the mistakes of one's predecessor (idiom)

lit. the cart in front overturns, a warning to the following cart (idiom); fig. draw lesson from the failure of one's predecessor; learn from past mistake

don't forget past events, they can guide you in future (idiom); benefit from past experience

(idiom) to warn against following bad examples; as a warning to others

to take sth as a warning (idiom); to draw a lesson from a case where things turned out badly