Again and again in novel-writing classes, they talk about “what the story needs to be told.” What details need to be there and what don’t. Their main point is that every scene and every moment of the book should be adding to the setting, characterization, plot, mood, etc. This is something I have had trouble with from the beginning.
The problem is that there are thousands of details about the setting and the characters that I need to know to write the book – by thinking about the history of the world or the protagonist’s past, I can make the world and character reactions more interesting and realistic (not to mention less predictable). How can I know who the characters are if I haven’t thought about their lives so far? Their past experiences with similar situations shape how they react to new ones. Maybe, I don’t know their whole story exactly, but without at least some of it, I wouldn’t know how to make them act at all.
There’s nothing wrong with that, and, honestly, I think that’s how writers build believable, interesting stories.
So, yes, those details are important. That doesn’t mean the reader needs to know them. Going into detail about how the town was founded may be interesting to you, but moments like that are pauses in the plot. If there are too many of them, the momentum for the climax can fizzle and die. Really intricate plots may be able to use more, and sometimes you can get away with more at the beginning of the book before the plot has gotten moving too much. At the same time, I know plenty of people who couldn’t get past the first chapter of Tolkien’s The Fellowship of the Ring because it was about the history, not the plot (honestly, I skipped that chapter the first time I read it as a kid).
The more character and world-building you’ve done, the harder it may be to avoid moments like that. The details that make the world work can be really exciting to the author, especially with science fiction and fantasy where more of the world is made up. I know when I think of a cool tidbit about the history of a fantasy world, I really want to share it. But you want to know a secret I’ve found? If I really, really want to share it…
I make it important to the plot.