system
Given the following post, respond as if you're commenting on Reddit:
human
[General] Iron vs. Magic

Why is iron so commonly considered "antimagic"? Not just spells, but also many supernatural beings are weak to it.
gpt
There is the theory that in early history during the Bronze Age and earlier, mankind was more primitive and feared the supernatural. The Bronze Age was when they still regularly forged metal weapons, armor and tools from the softer bronze, but the Iron Age began when mankind became more industrious, using more advanced scientific techniques to refine metals, to get more purified and stronger iron. This advancement revolutionized metalworking, caused cultural growth, and mankind was not as fearful of the supernatural as they were taming and conquering nature. Iron made for better weapons, horseshoes, ploughs, etc. Being less reliant upon their belief in the wild supernatural coincided with their reliance upon the controllable iron. The story of iron keeping fairy and demon away and obscuring magic became commonplace.

On a side note, the belief that Silver has effect on certain creatures of the night like undead and werewolves may be dependent upon the fact that historically silver in considered a lunar metal affiliated with the moon, while gold is a solar metal affiliated with the sun.