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(As @ChrisSunami said, the author should know more than the reader does. I am writing about what to include in the text) The question is reversed. The proper question is "What information about ...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/30738 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
(As @ChrisSunami said, the author should know more than the reader does. I am writing about what to include in the text) The question is reversed. The proper question is "What information about a fictional world is NECESSARY?" And the answer depends on the length of the piece. If you are writing short stories, the answer is "as little as you can possibly get away with." Every word counts. If you are writing a novel, the basic rule is still to only include information that has a purpose, but you can have other purposes than just advancing the plot. Building an atmosphere is perfectly valid. Rounding out a character is perfectly valid. Just don't dump all the information on the reader in one big wall of text; sprinkle it lightly throughout the text. Another important aspect is knowing who the narrator is. The reader doesn't necessarily need to know, but you as author _must_ know who the narrator is! Keep the text consistent with what that narrator knows and cares about.