Achilles' Heel, Origin and meaning

To have an Achilles’ heel implies that one has a vulnerable point. If this vulnerable point is attacked it will bring about the ruin of a person, country, object or idea, irrespective of any inherent strength.
In Greek mythology, this referred to a physical weakness. Modern usage is more symbolic for the downfall of virtually anything due to an inherent weakness.
In the mythological sense, Superman had an Achilles’ heel as in kryptonite. In the modern sense a marketing plan could have an Achilles’ heel if for example one was reliant on poor salesmen.
Origin is from Greek mythology. As a baby, Achilles was dipped in the river Styx by his mother to make him immortal. During the dunking process his mother had to hold him by the heel, and this part of his body, was covered by her hand, and no contact was made with the water. This became his vulnerable spot. He was invulnerable except for his heel.
Achilles excelled during the Trojan War, specifically during the final stages. After he had killed Hector, Achilles was killed by Paris, with an arrow to his heel. Some sources say the arrow was poisoned.
Achilles therefore, considered immortal, was killed via his heel, his only weak point.