Achilles’ Heel
Etymology
From the Greek hero Achilles, dipped as an infant in the River Styx by his mother Thetis to make him invulnerable — but held by the heel, which the water never touched, and where a poisoned arrow later killed him. Notably the heel-dipping detail is post-Homeric, appearing in Statius’s "Achilleid"; Homer never mentions it. The phrase now names any lone point of failure.
noun phrase · /uh-KIL-eez HEEL/
A single fatal weakness in an otherwise strong person or system.
What it names
A precise handle for the one vulnerability that can bring down something formidable — not a general flaw, but the decisive one.
Example
The company’s reliance on a single supplier was its Achilles’ heel when the factory flooded.
Related idea
A linchpin is the part that holds everything together; an Achilles’ heel is the part whose failure brings everything down — the difference between load-bearing and vulnerable.
See also