Depends

We are never told how much depends on the wheelbarrow the poet, William Carlos Williams, wrote into fame.

 so much depends
upon

a red wheel
barrow

glazed with rain
water

beside the white
chickens.

Depending on who we are and our background, a good deal depends on it.  The dynamic is set in motion with four words.  In similar fashion, depending on the length of the medium, say short story or novel, a certain amount depends on notes you sometimes see from an editor on a manuscript of yours or, conversely, the initials n.s. you sometimes put in the margin of a manuscript or a proof when you are the editor, addressing the author.

N.S.  Narrative summary.  Telling the backstory.  If our story happens to be one of the more popular short stories, Poe's "A Cask of Amontillado, we see all too soon what's at stake and how much depends on the narrator's response to those things.  

We get a description of the circumstances that caused the narrator to first vow, then plot revenge.  We still have only the merest idea of the "thousand injuries" the narrator had borne, and you would think the author would wish to give us a greater clue regarding the nature of the insult.

"THE thousand injuries of Fortunato I had borne as I best could, but when he ventured upon insult, I vowed revenge. You, who so well know the nature of my soul, will not suppose, however, that I gave utterance to a threat. AT LENGTH I would be avenged; this was a point definitively settled -- but the very definitiveness with which it was resolved precluded the idea of risk. I must not only punish, but punish with impunity. A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong."

The backstory or narrative summary is there in the opening clause, settled into place by the end of the first sentence.  We know the narrator is bent on some form of revenge, for a more or less generalized bill of complaint.  The fucker insulted me.  Now, he was going to pay for it.  

This is now more than a toe in the literary waters of the twenty-first century.  This is time to recognize how story has evolved. True enough, there are those who still find it convenient to begin their narratives with a summary of things leading up to it.  "Those" are authors who truly fit the description implied in the term "Grandfather clause;" they are holdovers from another time.

Story begins now with movement, action, or a planning session in which the furniture may be literally tossed about or figuratively shunted into a different place.  Story begins with dramatic action to the point where the reader is caught up in someone's web of circumstances.

Later, after we've become intrigued by what's happening in the present, we can pause for a moment to catch up, to be brought to realize how all "this" came to pass.  Now, the planned action either makes sense or is undercut by someone who wonders what we were thinking, which is, Why would anyone proceed with such a plan?

With such questions flaring up before us, we might be willing to look at some narrative summary, but not a moment before.  Suffice it then to say of n.s., "it is the dramatic foundation for the present-time action of the story and it is the reason why the characters behave as they do."

If story takes place more in the past than in the present, something is wrong; the narrative should begin farther along the orbital path.  In some ways, you remind yourself of an archaeologist, digging into past events, trying to ferret out some kind of life cycle for the artifact at hand.

We may need to know how clay is not native to the present area, has to be bartered for, either in its raw form and, thus, shaped and fired here, or bartered for in its present state and in consequence worth a good deal more.  What did Grandma give up in trade goods to get this pot?

All these are relevant, but the last thing we need to know are the physical properties of clay, where the clay for this pot was dug, and how it was fired.

Our goal is to embrace in story, not embalm in detail.