實用口語:如何說"致命弱點"

One's Achilles' heel（致命弱點）

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Weak or vulnerable point; fault, esp in sb's character, which can lead to his downfall.

致命弱點；（尤指某人個性中可導致一敗塗地的）缺陷。

關於Ahilles：

【希神】阿基里斯（除腳踵外，渾身刀槍不入）

When Ahilles was an infant, his mother tried to make him immortal by bathing him in a magical river.
當阿基里斯還是嬰兒時，其母親爲了使他永生而在神祕河裏爲他洗澡。

請看例句：

Vanity is his Achilles' heel.

虛榮自負是他的致命傷。