ACHILLES’ HEEL- the one weakness or flaw in one’s otherwise strong character.
Usage- My science and math are quite strong but English is my Achilles’ heel.
Story- This is from ILIAD from the Greek poet Homer. Achilles was a great hero and warrior. However, he had one weak spot the heel of one foot. When he was a baby his mother wanted to be certain that her son could never be harmed, so she dipped little Achilles upside down in the magical river Styx. Whenever the water touched her body he became invulnerable. But since she was holding him by his heel, that part of him never got wet. Years later Achilles was killed in the Trojan War by an enemy who shot a poisoned arrow into his heel.