I'm in the middle of writing the first book in what I had always imagined would be a trilogy. Now I'm starting to think that the trilogy idea may just have been a default. I mean, series of books come in threes, right? That is, unless they're really going for broke and wind up with 6+ instalments... This got me thinking, is there any plot/flow-of-the-story related reason for this tendency towards trilogies, or do people just like the number three?? Or, perhaps, three is just where writers end up when they originally plan on writing one book and it just, uh, expands . Thoughts? Similarly, is a duology (bilogy??) some sort of story format faux pas? Why are there so few two book series out there?? Are we all just stuck in the rut of tradition?