Achilles was a powerful ancient Greek Hero, who is most well-known for his participation in the Trojan War and his heel which caused his infamous downfall. Although only a story, Achilles' Heel presents a lesson that we can all take away from this tale: No matter how strong one maybe, one will always have weaknesses that will bring devastating consequences if not brought to light.
To understand how Achilles' Heel gained its reputation, we must first understand Achilles' story. Thousands of years ago, a titan named Thetis gave birth to a baby boy, Achilles. Although his mother was an immortal Titan, his father, Peleus, was not, therefore Achilles himself was considered "mortal." Thetis wanted to grant Achilles immortality and dipped him into the River Styx, a river that separated the mortal realm from the underworld. Because of this procedure, Achilles' physical body became near-invincible, becoming an unstoppable force in the Trojan War when he grew up.
However, because Thetis held onto Achilles' left heel as she dipped baby Achilles into the Styx, his heel did not make contact with the immortal powers of the river. Thus, when a stray arrow in battle found its mark in the left heel of the Myrmidon Hero, Achilles died. The most powerful warrior in the Myrmidon Kingdom succumbed to a stray arrow that hit his left heel.
So, how can we apply the story of Achilles' Heel to our world? Achilles only died because he was unaware of his heel - his biggest weakness. We too will face similar consequences (although hopefully not as severe as death) if we let ourselves become unaware of our flaws, whether it may be procrastination, dishonesty, laziness, etc. Achilles couldn't overcome his weakness because he didn't know about it, but once you know about yours, your entire life shall be within your hands to change for the better.