But every game has to have a world in which it exists. Over the years I've slowly cobbled together my own mythology. The same major guilds, religions, kingdoms, exist all the time, but the permutations which I've arranged them in change from campaign to campaign. There is, of course, always room for expansion. If the kind of story I tell necessitates some kind of entity that doesn't exist, the mythology changes. It grows.
Perhaps someday I'll write a lot of this stuff down to set the record straight but For now I enjoy the way the story of my world changes every time I tell it, like a folk tale or a comic book.