There are thousands of good reasons why magic doesn't rule the world. They're called witches and wizards, Magrat reflected, as she followed the other two back to the road.
It was probably some wonderful organisation on the part of Nature to protect itself. It saw to it that everyone with any magical talent was about as ready to cooperate as a she-bear with a toothache, so all that dangerous power was safely dissipated as random bickering and rivalry. There were differences in style, of course. Wizards assassinated each other in draughty corridors, witches just cut one another dead in the street. And they were all as self-centered as a spinning top. Even when they help other people, she thought, they're secretly doing it for themselves. Honestly, they're just like big children.
Terry Pratchett, Wyrd Sisters (via Magrat Garlick)
this was just so funny to me. I like that Pratchett never fails to emphasize that these social classes of characters aren't inherently good nor bad. They have their flaws and different ways of dealing with each other and the world. It's very human and therefore very grounding and entertaining.