I read and hear a lot about “story arc” these days.
I confess I don’t really know what it means. As near as I can tell, it is more or less the same kind of thing as the “dramatic structure.” It could be the “three-act structure” or maybe the “five-act structure.” Or even the “hero’s journey” structure I used to hear a lot about, but not so much anymore.
It all comes down to (as near as I can tell) what happens to your character(s) between the beginning and end of your book. How they change, and what changes them, or something like that.
Why this sort of thing needs a name, I don’t know. But “arc” does not seem to me a very good name. I see an arc as a curved line connecting two points. But stories seldom follow a curved line. They go up and down, down and up, sometimes sideways, and sometimes they go backward as you move along from page to page. Now, some may say this is all part of the “arc.” But, if your line isn’t a curved line connecting two points, is it still an arc?
Maybe it is. I don’t know. All I know is that your characters should (and will) decide how the story goes. And if you let them, they’ll blaze a much better trail than a carefully plotted “arc.”