The phrase “Achilles heel” means a person’s weak point, physical or emotional. Such a weakness, in spite of overall strength, often leads to the person’s downfall.
In Greek mythology, when Achilles was a baby, it was foretold that he would die young. To prevent his death, his mother, Thetis, took Achilles to the River Styx, which was supposed to offer powers of invulnerability. She dipped his body into the water but, because Thetis held Achilles by the heel, his heel was not covered by the water of the magical river. Achilles grew up to be a man of war who survived many great battles.
An alternate myth is that Thetis treated him with ambrosia and burned away his mortality in the hearth fire except on the heel, by which she held him. Peleus, his father, discovered the treatment and was alarmed to see Thetis holding the baby in the flames, which offended her and made her leave the treatment incomplete.
The death of Achilles is predicted by Hector in Homer’s Iliad, but it does not actually occur in the Iliad. It is described in later Greek and Roman poetry and drama concerning events after the Iliad, later in the Trojan War. In the myths surrounding the war, Achilles was said to have died from an arrow wound to his heel.
Although the legend is ancient, the phrase wasn’t seen in English until the 1800s. It is used as a metaphor for vulnerability, as in this early citation, an essay by Samuel Taylor Coleridge in The Friend; a literary, moral and political weekly paper, in 1810.
The connection between Achilles and heels was called on when the tendon at the back of a human heel was named the Achilles’ tendon. The oldest-known written record of the tendon being named for Achilles is in 1693 by the Flemish/Dutch anatomist Philip Verheyen. In his widely used text Corporis Humani Anatomia he described the tendon’s location and said that it was commonly called “the cord of Achilles.”
I would guess that every individual has an Achilles heel. I think mine is food, which I love rather too well. When my mother dunked me in the River Styx, she must have held me by the teeth.