People are using the term "kryptonite" with increasing frequency these days, in the sense of "weakness" or "thing which is harmful or deadly or terrifying to me", as in, "I'm claustrophobic, so elevators are my kryptonite." This is understandable, given the general public's notion of kryptonite as the substance that can weaken and kill Superman, but it is incomplete and misses what I call the irony of kryptonite.
To understand this irony, we must first understand what kryptonite is, in the world of Superman. The child, Kal-El, who would grow up to become the Man of Steel, was sent to Earth in a spaceship by his parents to escape the destruction of his planet, much as Moses was set adrift on the Nile to escape the destruction decreed by Pharaoh. The planet Krypton was transformed by its nuclear death into the substance kryptonite, a green, glowing, radioactive death-dealing horror to Superman.
Here is the irony. The very ground of his home planet, which, in the natural course of events would literally support him and grow the food which would sustain him, has become toxic to him. Even worse, the explosion of Krypton resulted in the transformation of everything on the planet into this deadly matter. Books, trees, houses, sporting equipment, the very stuff of daily life, all became kryptonite. Not only has the ground which would have physically supported him on his homeworld become his deadly enemy, so have the things which would have supported him psychologically and emotionally. Imagine, for example, that Superman were to find his parents' wedding picture, or his favorite stuffed toy from childhood, somehow fallen to Earth. He might at first feel a wave of sentimental nostalgia as he remembered, if he could, the brief but happy time in the bosom of his now-gone family. Almost simultaneously, though, this would be overwhelmed by horrified realization of the threat to his survival.
Perhaps fate, or the universe, strives for balance. Superman has lost his biological parents, but he gained adoptive parents, the Kents. He lost his people and his planet, but he gained the people of Earth, his new home. He is arguably the most powerful being on Earth and beyond. Balance requires a weakness, and perhaps not simply a physical weakness, but an emotional one, as well. Not only can he not go home again, any significant exposure to his “home” will drain his strength and turn him into a green-skinned corpse. Finally, there is one last interesting piece of the puzzle. While it is generally known that kryptonite is deadly to Superman, but harmless to Earth-humans, what is sometimes not so well-known is that kryptonite is also harmless to a Kryptonian without super powers. That is, if Superman were to find himself on a re-constituted Krypton under its red sun, kryptonite would simply be an interesting green, glowing rock. Thus, kryptonite is a threat to the hero Superman, not the person Kal-El. The creation of a great hero requires a correspondingly great weakness.
The life of an ordinary person has more ordinary weaknesses. Fortunately, we have the inspiration of our fictional heroes, like the Man of Steel. As great a weakness, physically, psychologically and emotionally, as kryptonite is to him, he has never failed to overcome it, either on his own or with the help of others. Let this be our goal, too, in facing our own weaknesses.