陳陳相因

Originally refers to the way old grains a stockpiled in warehouses:

太倉之粟，陳陳相因，充溢露積於外，至腐敗不可食。 [Traditional Chinese poetry, trad.]

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太仓之粟，陈陈相因，充溢露积于外，至腐败不可食。 [Traditional Chinese poetry, simp.]

From: The Records of the Grand Historian, by Sima Qian, c. 91 BCE

Tàicāng zhī sù, chénchén xiàngyīn, chōngyì lùjī yú wài, zhì fǔbài bùkě shí. [Pinyin]

In the Imperial Granary, old grains are stacked upon even older ones and are in turn followed by more old grains. They overflow the storage and are exposed outside in piles, until becoming rotten and unfit for consumption.

陳陳相因

1. (figurative) to become stagnant or obsolete due to rigid adherence to tradition; to be devoid of any innovation