亡羊补牢 (Wáng yáng bǔ láo)

Literally: To mend the pen after the sheep are lost

Example: “虽然丢了一次数据，但现在开始备份，亡羊补牢，为时未晚。” — We lost the data once, but backing up now is better late than never.

English equivalent: Better late than never

Origin: From the Zhanguo Ce (Strategies of the Warring States), in the Chu section: the minister Zhuang Xin told King Xiang of Chu, after the king's losses, "To look for the dog once the hare is seen is not too late; to mend the pen once the sheep are lost is not too slow." The phrase means that it is not too late to repair the damage and prevent more.