<P> An 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 . </P> <P> 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, and dipped his body into the water; however, as Thetis held Achilles by the heel, his heel was not washed over by the water of the magical river . Achilles grew up to be a man of war who survived many great battles . One day, a poisonous arrow shot at him was lodged in his heel, killing him shortly afterwards . </P>

According to legend who fired the arrow that hit achilles in the heel his only vulnerable spot