system
Given the following post, respond as if you're commenting on Reddit:
human
[Game of Thrones] Why is dragonglass simultaneously the thing that made the White Walkers, and the thing that kills them?
gpt
I guess it's the Mount of Doom kind of arrangement. Something can only be destroyed by the thing used to create it.

For example, Axe of Dwarfish Lords also can only be destroyed in the forge it was created in. Although it has to lie in there for fifty years to finally melt.

Or like Superman - he was born on Krypton, yet pieces of krypton is the one thing most lethal to him.