Procrastination is his Achilles' heel, causing him to miss many deadlines.
Exposing his Achilles' heel made him an easy target for criticism.
Her lack of confidence was her Achilles' heel, hindering her progress in the competition.
His stubbornness proved to be his fatal flaw, leading to his downfall.
His arrogance was his Achilles' heel and ultimately led to his undoing.