One resource explains the whole world
Negative emotion leaks out of people and pools in the places where they feel it. Left alone, it takes shape and becomes hostile. Sorcerers work with the same substance deliberately, which is why the heroes and the monsters in this series are made of identical material and the story keeps pointing that out.
Once that clicks, most of the world-building follows: why schools train sorcerers in secret, why some locations are worse than others, why the strongest enemies are the ones formed from the fears that everybody shares.