 when he can't do long distances, for example. It has its origins in ancient Greek legend. Achilles was dipped into a river by his mother in order to give him a skin of armor and make him invulnerable to his enemies. But she held him by the heel, which didn't get covered by the water and became a weak point for him. He became this great warrior, but his arch enemy, a guy called Paris, discovered his weakness and killed him by shooting an arrow through his heel.