system
Given the following post, respond as if you're commenting on Reddit:
human
[Superman] Why does Kryptonite affect Superman?

It's just a rock from his home world, something he would have encountered every day had he stayed home.
gpt
It is a radioactive crystalline isotope of krypton which, due to decay into a lower element, emits some combination of free neutrons and some electromagnetic wave damaging to Kryptonians unique cellular structure.