Rule 21 of 24 · Chapter V — The Unseen Mass
Leave the mystery a little dark
Why this rule exists
Some things in a world should never be fully explained, because their power lives in their obscurity and dies in the light. The god whose nature is glimpsed but never charted, the ruins no one can read, the magic that works but not why, keep their grip on the imagination precisely because the mind cannot close them off. Over-explanation is a quiet vandalism, trading the vast for the merely complicated, replacing awe with a mechanism. Wonder and dread are feelings about the unknown, and the moment you hand the reader a complete account, you convert a mystery they could feel into a system they can only assess. A world entirely explained is a world entirely mastered, and a mastered world has nowhere left to be strange.
In practice
Decide which of your world's elements are mysteries to be preserved rather than puzzles to be solved, and guard their darkness. Show these things working without spelling out their mechanism, let characters wonder without answering them, and prefer implication and glimpse to full disclosure. Give the reader enough to feel the presence of a deeper order without ever charting it, and resist the fan's and the editor's pull toward the total explanation, which so often diminishes the thing it clarifies. When you feel the urge to reveal how the sacred or the terrible really works, ask whether the revelation adds wonder or merely subtracts it.
When it doesn't apply
Mysteries a plot promises to solve must be solved, or you break faith with the reader, so this applies to the atmospheric and thematic unknowns, not the dangling plot thread. Puzzle-driven stories, mysteries, hard science fiction, may owe the reader a full accounting by design. Know which of your unknowns are questions you have promised to answer and which are darknesses you are keeping on purpose.