Like many would-be writers, I have a half-conceived idea for a fantasy novel/series that I've been toying with for many years. As I've gotten older, the idea has matured with me, but I still don't think it's "ready." Most of the work I've done on it has been world-building. The main characters are pretty much all from the same culture (with slight regional variations), but as the novel progresses, the reader learns of the wider world in which they live, and learns things which challenge the assumptions made towards the beginning. In fact, the idea of holding on to one's own culture in the face of another is one of the major themes of the book. I know the general structure of each society. I have identified the "cultural heroes" that each group treasures (e.g., your George Washingtons and Albert Einsteins, the people who embody the values of that culture). I know the religion, the entertainment, the food. I've even traced how their languages are interrelated, although I have gone full-on Tolkien and invented them yet. I know which animals are important, for work and for pets. I've even invented the stereotypes that each culture has of the others, accents, and sayings. I'm sure that only a tiny fraction of this will make its way into the finished story, but I feel it's important to know in advance, since I can't really do "research" on these cultures, and I don't really want to make it up as I go along. The question is, where do I draw the line? At what point is the world building "done"? Am I using the world building as an excuse not to start the actual novel?