Most writers will tell you that your novel needs to have at least two major conflicts: an internal conflict and an external conflict. Main characters have to overcome both in order to win the day. Conflict drives the story and multiple levels of conflict make the story that much richer.
From what I've seen, in most genres people tend to focus on the external conflict. If you ask someone what the mystery they're reading is about, they'll likely respond by detailing how the detective has to find a killer before he takes another victim. On the back cover copy of an urban fantasy novel, you might read about the witch trying to stop a horde of demons from opening a portal to hell and destroying the world.
Those are external conflicts. Character A must battle Character B to save the day. And with all the witty dialogue and thrilling action scenes, what's not to love?
The internal conflicts, on the other hand, are frequently treated like subplots. The main character has to deal with those issues, sure, but more as an aside, or maybe as a step toward dealing with the external threat. The internal conflict usually isn't seen as a threat in and of itself. After all, saving the world is way more important that whether or not some guy ever gets over his fear of abandonment, right?
Internal conflict is hugely important. It's what the reader really connects with when a good story draws them in. It's what humanizes the characters and makes the readers care about what happens to them. Without a strong internal conflict, the story is just so many words strung together on a page, the writer yammering on about things that didn't really happen to people who don't really exist.
And internal conflict is also one of my. . . opportunities for improvement as a writer. One of the interesting things about plotting my current novel instead of pantsing like usual is that I've found a number of holes in my process. One such hole is that when I was asking myself "what happens next?" I was only focusing on the physical challenges, where the characters go and who they fight and such. I'd never considered that what happened next might be happening on the inside.
In other words, I was only focusing on the external conflict and treating the internal conflict like a subplot. So I've been studying internal conflicts a lot recently. And I've been studying them in a place you might not expect: romance novels.
Don't make that face. Romance novels have gotten a bad reputation. "They're formulaic." "They're silly." "They're just mommy-porn." (That last one pisses me off for a whole bunch of reasons I'm not going to get into here.) What complete and utter crap. I know because I used to say those same things, and I was wrong.
There are plenty of formulaic and silly romance novels out there, but there are also plenty of science fiction novels that fit that bill too. And mysteries and thrillers and fantasy and even literary fiction. Formulaic and silly are not attributes exclusive to the romance genre by any stretch of the imagination.
But just like all those other genres, there are a lot of great romance novels too. And in addition to being very entertaining reads, the great romance novels can teach you a whole lot about internal conflicts.
Romance novels run the opposite way from other genres in terms of conflict. The internal conflict is what drives the story. The main characters might be trying to open a restaurant together or trapped by a snow storm or involved in a legal battle over a priceless work of art, but at the end of the day the story is about them getting over whatever is wrong inside their own heads and getting together.
With the focus reversed, the dynamics of writing a good internal conflict become easier to spot. I've learned a ton about how to write changing emotions. How to show a character lying to themselves. How to create a character who might just rationalize their whole life away if they're not careful. All from reading those silly, formulaic novels that are really just mommy-porn anyway. ;-)
If you want to learn how to write a big bloody battle scene from the perspective of a soldier on the front line, you're probably not going to find that in your average romance novel. But if you want to see how to make a character realize he doesn't trust anyone, least of all himself, a good romance novel may just be your best bet.