An Achilles' heel or Achilles heel is a weakness in spite of overall strength, which can lead to downfall. While the mythological origin refers to a physical vulnerability, idiomatic references to other attributes or qualities that can lead to downfall are common.
The story goes something like this: After Achilles was born, his mother wanted to protect him from harm. She held him by the heel and dipped him into the river Styx. In Greek Mythology, the river Styx was located in the Underworld and had special powers. Achilles became invulnerable everywhere but at his heel where his mother held him.
