I'm writing a novel... for which I have the premise, I have the introduction, the main characters, the main conflicts ... minus one. I lack ONE thing that will move the novel into completion and I have no idea what that thing is.
So I all I can really do is sit and think, and that prevents the actual writing from occurring. Because I can't really write when I'm not impassioned with ALL the ideas, including that one thing that will make or break this book.
This book must be a tool; I can't waste so much time and energy on one of those "beach books," which have no real quality to them. I refuse to write anything in that context that won't have some sort of positive effect, call something into question or promote a necessary change.
Do we have any novelists or writers who can relate with what I'm saying?
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I understand perfectly. You want the reader to take something away from your novel.
I'm not sure if you're still stuck or if you've found it, but in my experience, I've found that just throwing yourself into it without trying to have all the ideas sorted out can help. Writing in itself is a learning experience, and somewhere along the line, you'll learn what it was that you were looking for.
And for all that you wrote before that may not be what you need it to be? Rewriting is a wonderful tool for that. A novel isn't completed until it has been rewritten several times over, after all.