Just because it isn't in the story as shown doesn't mean it didn't happen.
By that I mean storytellers need to know the backgrounds and histories of their characters even if those parts of their past are not told in the tale at hand.
As an example, in the movie Back to the Future (and its two great sequels), a high school boy is friends with a crazy (no no, crazy is too harsh... eccentric? wiley? frazzled?) scientist with a doctorate who specializes in wacky inventions and has a Rube Goldberg Machine to feed his dog.
The fact that they are friends is pivotal to the story... and when the movie begins, Marty is entering the Doc's (he calls him Doc) "lab"/garage. Thus, from the start, they have an established relationship. There's no denying they're good friends. Even so far as the Doc telling Marty to meet him in the parking lot of the mall at 1:15 in the morning and Marty does it without question! We're to accept their friendship and go on with the adventure.
However, fans have always wondered... how does this unlikely pairing exist? Why does a teenage boy (who has aspirations of being a rock star and problems at home [like so many of them out there]) with a girlfriend choose to spend his time with a (ahem) strange Doc of weird science? Likewise, why does a white-haired scientist who's been [seemingly] unsuccessfully creating things since at least the 1950's such as a mind-reading helmet (which looks more like an Erector set dome with hair curlers) want to have an angsty kid hanging around? Oh sure, plenty of answers can exist. And the speculations ran rampant. Everyone had their own idea of this duo's dynamic beginnings. But what's the truth? Which one is correct? IS one of them correct?
It turns out yes, there is a definitive answer. Why? Because the truth is that director/writer Robert Zemeckis and writer Bob Gale, as well as the actors and others involved with creating the film had their own version of the origins of the friendship between Marty McFly and Dr. Emmett Brown. Why? Because as storytellers, they needed to know. It would affect how the characters reacted, hence the actor's performances. And it had to all come across as believable. Which it did... I don't think anyone ever called "foul" on their friendship, just a "Hmmm...what's the deal?" It didn't present it self as problematic. Rather it became intriguing.
How do we know there's a definite tale of how they met and became friends? Not so long ago in the media news, we were treated to the insight by Robert Zemeckis himself. You can read it here if you're curious.
My point, then, is that a story exceeds the boundaries of the medium in which it is told. Just because a piece of the characters' or situation's history is not revealed in the book, the author(s) must have an idea of what it had been. It's not possible to create a successful tale and not know the backstories. For knowledge of it will shape how the bits that ARE shown play out. It helps to have the intesity of the emotions and situations bolstered by the past.
Think of your own relationships. Are they not affected by what had been forged long ago? If we were to tell an adventure from your life as a book, would it not behoove us to feel the fervor of what had been to better understand the events and kinships that exist during said adventure? Of course.
Then again, it's not always important to actually know in the storytelling. After all, we're telling specific events. The audience can easily be bored by every detail of the past. In the case of Back to the Future, for instance, we don't need to waste precious movie time with the events that Zemeckis described as the start of their friendship. They're not part of the tale being told. Imagine if it the film showed that scene. We'd then have to show the progression, the build of how they came to care about each other... and thus it would take "forever" to get to what the movie is really about. But again, these previous moments in time shine through in the background, for as I said, no one questions their being pals.
So it's up to an author to realize what information is pertinent to the story at hand. But it's also up to the author to know what's pertinent behind the scenes, even if no one wants to or needs to know. Yet if you do it right, they will want to know. Any writer who cannot tell you about the extraneous bits of their story isn't doing the job. That's not to say that every single bit of minutia of has to be known, but by golly, if asked, the answer should come springing forth. And if it doesn't, don't fear, the characters know... just ask them.
I am a fiction writer. Mostly I compose in the Urban Fantasy genre. When asked, I usually liken it to "The Twilight Zone" - extraordinary events emerging in everyday life. I graduated with Honors in Creative Writing from Knox College in 1993. Obviously I also scribble cartoonish drawings.
Here you will find my nonfiction - the place for me to share my thoughts with you, keep you posted on upcoming events and allow me to interact.
If you wish to leave a note, use my cartoon quill and ink.