My theory on backstory is that it is essential for you to know it intimately. Your reader, not so much. What is crucial is that whatever universe your characters move through is consistent with that back story and that they behave accordingly. Much can be intuited simply by seeing them interact according to the rules of that universe. Crucial details, when needed, can be salted through the present-day narrative, action and dialogue. You never need as much as you think, as long as you have a real story unfolding in the present.
Which is the strongest argument against back story: stories happen
now. No matter how dramatic those events from the past might seem, you can never channel that energy to propel present events forward. The past is static, inert. If you spend too much time there, your characters, and your reader, will be standing around, looking at their watches, wondering when you’re going to get back to their reason for being there I the first place. If you find yourself continually drawn to your back story, perhaps that’s the story you should be telling instead.
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