殷鉴

noun

lesson from past failures that serves as a warning to later generations; historical precedent of downfall

Derived from the Classic of Poetry (Shijing): "The mirror of Yin is not far—it lies in the era of the Xia successors." Originally referring to how the Yin (Shang) overthrew the Xia, warning that the Yin people should take the fall of Xia as a lesson. Later extended to mean any cautionary example from history.