I have frankly been annoyed when my writing friends talked about backstory. I didn’t know what they meant and I took it to mean it didn’t mean anything. It was just one of those fancy terms tossed about in writing workshops but like other trendy constructions, it meant nothing at all.
But I picked up a book, Breathing Life into Your Characters by Rachel Ballon, Ph.D. and she pointed out that readers need to know why a character is motivated to behave as he/she does in the story.
For example, one of the major characters hasn’t dated in a few years. Until I picked up the Ballon book, I didn’t realize that I would have to explain how and why this character behaved so differently from cultural norms. Once I opened a file and put the rest of his story there, I realized I felt more comfortable writing about him. He did have a good reason for not dating, and that behavior makes his more memorable as a character.
I did that with the second major character as well, realizing that his very crazy choice of careers made sense in view of his situation. Again, it went into the same file as the first backstory.
In other words, backstory is simply the answer to why a character behaved as he/she did. Without this understanding I might have developed writer’s block because the story, wouldn’t make sense. In time, that would have interfered with the narrative flow.
The next challenge: to learn description, when to use narrative and when to use dialog. I tilt very strongly to the dialog side which is as much of a failing as relying exclusively on narrative.