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It happens. When the Moon is in the seventh house, and Jupiter aligns with Mars, or whatever. You have a creative idea and it translates. Verse, music, prose, it's a product of the inspiration that grabs you and makes perfect sense at the time, like a dream that lets the new day dawn with a feeling of elation.
Writing a novel is a lengthy process and completing the manuscript can take anything from a few months to several years. That's a long time to maintain the spark of inspiration that initiated the novel idea. Then editing is required, adding time and over-familiarity. At the end, when the work is ready to publish, an author often just wants to get done and over. Somewhere, deep inside, the ember of inspiration remains but the author has long since moved on to kindle another fire.
I get the impression that mainstream authors birth their creations and only revisit them when forced to do so by interviewers or high profile literary reviewers. Ideally they don't even read the critics' viewpoints and certainly never scour online reviews at Amazon or Goodreads. Not so the independent authors! Reader reviews are a valuable tool for indies to gain exposure and garner referral sales.