achilles' heel

What is the origin of the idiom "Achilles' heel" and when to use it?

The idiom "Achilles' heel" has its origins in Greek mythology where the hero Achilles was invulnerable except for his heel, which was his one weakness, Achilles was eventually killed when an arrow struck his heel, which led to the popularization of the idiom. Today, the phrase "Achilles' heel" is used to describe a person's one weakness or vulnerable spot that can lead to their downfall or failure.