I'm having frustrations right now with my current project. I have a world, complete with geography and politics and competing religions. I have a cast of characters, major and minor, with backstories of varying complexity. I have a structured magic system.
But I don't really have a plot. I have a vague idea of the antagonist and what she wants, but I don't know how she's going to go about it. I don't know what my main character wants, either, other than keeping her family together. Obviously these are huge missing pieces which usually by this point in the plotting process have fallen into place. Maybe I'm overthinking it, because I wouldn't do this much pre-planning with fanfic, but this is different, and I want to know what I'm writing before I start writing. I guess I'll just have to keep mulling it over until inspiration strikes!