Rúguǒ bù cóng guòqù jíqǔ jīngyàn, ér hòurén āi zhī ér bù jiàn zhī, bēijù huì chóngyǎn.
If we don't learn from the past - 'later people mourn them without taking warning' - tragedy will repeat.
Tips
history
From the Late Tang poet Du Mu's 《阿房宫赋》 (825), a fu-prose piece on the fall of the Qin: 秦人不暇自哀，而后人哀之；后人哀之而不鉴之，亦使后人而复哀后人也 (The Qin had no time to mourn themselves, so later ages mourn them; if those later people only mourn without taking warning, they too will make still-later people mourn them). Du Mu's circular warning - mourning without learning guarantees repetition.
usage
Inseparable from the fuller sequence 秦人不暇自哀 / 而后人哀之 / 后人哀之而不鉴之 / 亦使后人而复哀后人也. 哀 = to mourn, lament. 之 = them (object pronoun). A favored quote in Chinese historiography and reform debates.
