moment of truth 
关键时刻, 决断时刻, 紧要关头
斗牛中的最后一剑
MEANING:
noun: A crucial point; a turning point; a decisive moment.

ETYMOLOGY:
Loan translation of Spanish el momento de la verdad. In bullfighting, the moment when a matador is about to kill the bull is called el momento de la verdad.

USAGE:
"The moment of truth has arrived for the euro. The 16-nation monetary union faces its greatest test Wednesday in Athens, as the Greek government orders last-ditch radical cuts in hopes of preventing the eurozone's first debt default and a wider financial and monetary disaster."
Doug Saunders; Greece Set to Impose Austerity Measures; The Globe and Mail (Toronto, Canada); Mar 2, 2010.

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A THOUGHT FOR TODAY:
To write that essential book, a great writer does not need to invent it but merely to translate it, since it already exists in each one of us. The duty and task of a writer are those of translator. -Marcel Proust, novelist (1871-1922)