Today’s Wonder of the Day was inspired by Reece. Reece Wonders, “How did Achilles die?” Thanks for WONDERing with us, Reece!

Do you love superhero movies? A lot of kids like Superman, for example. What's not to like about a superhero who wears a cape and can fly to save you from grave danger at a moment's notice?

Of course, you might run into difficulties getting rescued if you're toting around a backpack full of Kryptonite. Why? The radiation from Kryptonite is the only thing that makes Superman vulnerable. Others might call it his Achilles' heel.

These terms — Achilles' heel and Kryptonite — are often used to describe a person's greatest weakness or vulnerability. We understand the meaning behind Kryptonite from our familiarity with the Superman character, but who's this Achilles person and what does his heel have to do with anything?

In Greek mythology, Achilles was the son of an immortal goddess named Thetis and a mortal man named Peleus. When Achilles was born, Thetis thought she could make him immortal by submerging him into the River Styx.

As legend has it, Thetis held Achilles by his heel when she dipped him into the river. Therefore, his heel was not touched by the magical waters of the River Styx and remained mortal and thus vulnerable.

Achilles went on to become a hero in the Trojan War. Tales of his heroics can be found in Homer's Iliad. Unfortunately, he was killed near the end of the war when he was shot in the heel by an arrow.

Over time, the term "Achilles' heel" has come to mean a vulnerability or weakness in an otherwise strong person. For example, a seemingly-unbeatable warrior might be brought down by his Achilles' heel, such as pride or love for someone.

Achilles also has his name attached to a part of your body that can be found at the heel. The Achilles tendon is the largest and strongest tendon in the body, stretching from the calf muscles down to the heel.

Despite its strength, however, the Achilles tendon is also prone to injury. Doctors speculate this is because of its limited blood supply and the fact that it frequently has high tension placed upon it, especially during walking and running.

So what is your Achilles' heel? If you're an athlete with a torn or ruptured Achilles tendon, it may literally be your heel! For others, though, it can be any one of a number of weaknesses or vulnerabilities, such as pride, impatience, laziness, selfishness, stubbornness, impulsiveness, fear, passivity, or aggression.

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