I'm an A student in math and science, but English is my Achilles' heel.

Meaning: the one weakness, fault, flaw, or vulnerable spot in one's otherwise strong character.

Origin: In the Iliad, the famous story about the Trojan War by 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. Wherever the water touched his body, he bacame 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.

指唯一的弱點，源自《伊利亞特》中的人物阿基琉斯，全身只有一個弱點——腳后跟。