When I spin together a world for a tabletop roleplaying game, I always make sure that I, at least, understand why the world works the way it does. I don’t need to know every single law of physics, magic, or society, and I have no interest in filling in every potential gap, but I make sure I know why things are in their current state. Most of the time, this is economics, politics, and society, the reasons people do things, what they want, and what their goals are. In one of my D&D games, this means that I had to know why the world exists in the state it does.