Though anatomical, "Achilles tendon" idiomatically denotes a critical weakness. Drawn from Homer's Iliad where Achilles' heel was his downfall, it symbolizes fatal flaws in strength. Poetry utilizes this for tragic irony, human frailty, and hubris, as in Auden or Eliot's explorations of mortality. It enriches verses on heroism's limits, personal Achilles' heels in character studies, or societal vulnerabilities, providing mythic depth to themes of imperfection and inevitable fall in epic, dramatic, and confessional poetry.

Although literally anatomical, this phrase carries mythic force because of Achilles, the near-invulnerable Greek hero whose heel became his fatal weakness. In poetry it can condense heroic strength and hidden fragility into one image. It is especially useful in tragic, epic, or psychological contexts where a character’s greatness is undone by pride, love, fear, jealousy, or one small overlooked flaw.