From
杜牧《
阿房宫赋》(Du Mu, Late Tang, 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.