Achilles' heel

An Achilles' heel refers to a weakness or vulnerability, despite overall strength. The term originates from Greek mythology, specifically the story of Achilles. As an infant, Achilles was dipped into the River Styx by his mother, Thetis, in order to grant him invulnerability. However, because she held him by his heel, that part of his body was not touched by the water and remained mortal. Achilles was eventually killed by an arrow to the heel, proving this weakness fatal.

Therefore, an Achilles' heel represents a crucial point of failure or a fatal flaw that can lead to downfall, even in someone or something otherwise powerful and robust. It is often used metaphorically to describe a particular weakness in a person's character, a system, a strategy, or an organization. This vulnerability can be exploited by others, or it can lead to internal collapse.