We often talk about external and internal conflicts in stories. The idea of having both - i.e. having an external challenge the protagonist has to deal with, but also giving her or him some internal struggle - is a very important one. Only having external conflict makes the story seem flat; only having internal conflict makes the story feel like nothing's happening. It's great to have both! Moreover, having the external conflict's arc line up with the internal conflict's arc so that the two can be resolved by the same climactic event is also really great. It gives the story dimension and drive, and certainly lifts it above what it could have been with one arc type alone.
But there may be still more you can do.
Stories don't just have one or two arcs total. They have many. Any time you see a progression of change within a character, or a series of three (or more) events that occur on a related topic with a timeline of development, you have an arc. You can make sure to put in an arc of one type or the other.
For example, I recently wrote a story about a girl who was going crazy trying to study for her college entrance exams, who runs afoul of some ghosts. I knew she had an arc relative to her success on the exams, and an arc relative to her personal sanity. Those two were solid. But the ghosts didn't have much of an arc at first, and I was struggling to give them one. Then I realized that this was a fantasy story, so it would be far more meaningful if my character encountered some kind of supernatural danger that threatened her directly - and that was where I got the idea for the character arcs of the ghosts. Suddenly, with an arc of supernatural risk that linked both to the ghosts and their purpose, and to the girl herself, the story came together and became more meaningful.
I've also been working on a story in my Varin world. The main character is Pelisma, a woman who has held a position of power but who is losing that - or worries about losing that - because she has also been going blind. [internal] She is also encountering a problem with a potentially dangerous type of organism that has inexplicably become attracted to her. [external] I had the story completely drafted, but it still felt like it was missing something.
One of the things I've noticed when I speak to friends who are authors - at least the ones who tell me about their fan mail - is that readers love when there is something in the story that is relevant to their own lives. This can be a "message," if it's handled well. (I know messages in stories can be really annoying when done badly, but they can be done deftly, too.) A story that evokes real issues in the real world has a kind of "lift," or extra dimension, that it would not have without that.
I decided that Pelisma's story was missing that special "something" to link it back to our own world, and give readers a sense that in Pelisma's experience, they were seeing something from their own lives. When I thought back over what I had written, I knew that loss of competence was something people could probably relate to in a distant way, but that it didn't really tackle anything deeper (and certainly didn't articulate with disability issues in a way I would have liked, since it treated her blindness as a "problem" that could potentially have some "solution"). On the other hand, there were hints in the story of another issue. Pelisma is also struggling with strong surges of emotion, such as frustration and helplessness, as she deals with the changes in her life. Overall, this leads her to feel that she doesn't have the control over herself that she once had. She feels as if her competence and self-control in the emotional arena have been compromised... and that to me was far more interesting.
Pelisma's story ends up with three arcs: 1. the external threat, 2. the internal issue of whether she can continue to do her job and keep her purpose in life, and 3. the additional internal issue of whether she is becoming "emotional," and whether she should consider that a weakness. The word "emotional" in our own world is definitely one with negative connotations, and is central to disputes about femininity, masculinity, and bias. I'm excited about strengthening that arc in the story, because I think that this will create an extra dimension that will take the story from "interesting" to "compelling."
What kind of arcs in your story might readers relate to on a personal level? What real world issues might it evoke?
It's something to think about.