Ok. Never mind. Having a "sunny disposition," is not a superpower. Or if it is, the "kryptonite" to be used against it is anything bad happening, and anything bad happening happens all the time.
So this (now in quotes & italicized) "superpower" can easily be played with, toyed with, and defeated. Let's just say there is nothing quite as bitter and spiteful, and vengeful, than a disappointed idealist. Those are the folks who prop up other folks against the wall to be shot down like dirty dogs.
So maybe a sunny disposition is just a front. A false front. Not bone-deep, not in the DNA, but just a thin veneer, a wrapper, like cellophane, or cheap wood-paneling; push hard enough and it tears, cracks and crumbles into a million tiny pieces.
You can always look on the sunny side. But it takes effort. And energy. And some times it's hard to conjure up. Then the darkness does come knocking. And the light and dark does their little yin/yang dance together. And neither the light, nor the dark win. They just dance. Eternally.
So, let's not get cocky, or overstate the case. Lean to the light. That's really all we have. A lean. A tendency. A glimmer. Nothing super about it, not so powerful either. A tiny thing. A spark. A flame. An inclination. That's it!
They say "It's always darkest before the dawn." So, if we believe them, there is the promise of light. Sometimes that is all we have, a promise of a glimmer. Hah! Run with that!