罪zuì魁kuí祸huò首shǒu

Literal: chief of the crime, head of the disaster
Figurative: The chief culprit behind a crime or disaster; these days it very often names the main cause of a problem, with a note of blame.

Where does 罪魁祸首 come from?

It does not come from a specific anecdote; it is two words of nearly the same meaning set side by side, a common device in idioms. 魁 is the ringleader, the one in front, and 首 is the head; 罪魁 is the chief of the guilty and 祸首 the one who leads or sets off a calamity. Together they insist on pointing to whoever is most to blame. Its home ground is law and chronicle, for the instigator of a revolt or a crime, but today it is used constantly in a figurative sense, for the main cause of something bad: sugar, phones, lack of sleep.

How is 罪魁祸首 used? Two examples

熬áo夜yè才cái是shì黑hēi眼yǎn圈quān的de罪zuì魁kuí祸huò首shǒu，买mǎi多duō贵guì的de眼yǎn霜shuāng都dōu没méi用yòng。
Staying up late is the real culprit behind dark circles; no eye cream will help, however pricey.
调diào查chá发fā现xiàn，这zhè次cì火huǒ灾zāi的de罪zuì魁kuí祸huò首shǒu是shì一yī根gēn没méi掐qiā灭miè的de烟yān头tóu。
Investigators found that the culprit behind the fire was a cigarette butt that hadn't been stubbed out.

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