When you are composing your story, you can add as much narration and backstory as you want. Feel free to cram in everything you see, hear, imagine, know, and wonder about.
You can do that because you are writing for yourself. Capturing lots of details and getting down the history can build a wonderful base for a convincing, layered, and rich story. The only danger you face in the drafting stage is slowing things down so much you miss the action and harm the pacing. Unless you fall in love with what you put down.
That's a real danger, and the most common flaw I see in manuscripts. You should never force any readers (including contest judges) to wade through big blocks of worldbuilding, flashbacks, memories, reflections, and descriptions. They may like all of these, but they come for the story and most commercial fiction proceeds at a brisk pace, moment to moment.
Why does slowing things down matter? Why does commercial fiction need to
consist overwhelmingly of action and dialogue in the present? Because
we like to identify with the characters. Since we live moment to moment,
any deviation from that in the world of the story is distracting and
distancing. It takes us out of the story.
Now, some narration and backstory needs to be there. A cardinal sin in writing is being unclear. Except in cases where you are deliberately raising questions (which happens a lot in some genres, science fiction probably leading the way), your readers should know what's going on. But they don't need to know as much as you do. I had the pleasure of hearing Candace Havens speak recently, and she referenced icebergs. The story your reader gets is the visible tip, while most remains hidden. Now, you don't have a full iceberg unless the portion below the waterline exists. (Meaning, the writer needs to know a lot more that is expressed in the story or doesn't work.)
For most writers, the hidden part of the story finds expression in exercises (like character building) and what pours out in the first draft. So the problem comes with a failure to deal with all the extras -- the parts that need to be out of sight -- in rewriting.
How to do that, to get the balance right, and to keep the story from being hobbled, is what I'll cover in the next post.