I'm always a bit baffled when people say Ron and Hermione had a smooth path in canon and fanfic just smooths out the edges. Their dynamic is a minefield of unresolved tension that fanfic writers love to detonate. You've got the whole pureblood versus Muggle-born cultural divide, which the books touch on but never fully explore from Ron's perspective—what's it like for him, with this ingrained wizarding worldview, to fall for the smartest witch who constantly challenges that very world? That's low-hanging fruit for angst. Then there's the class thing, the Weasleys being "blood traitors" but still old wizarding stock, Hermione's parents being dentists... it's a mess of unspoken social friction.
A lot of stories I've seen dig into Ron's insecurities much deeper than the books did. It's not just about Harry; it's about feeling perpetually overshadowed in his own family, then having to measure up to Hermione's academic brilliance and moral certainty. The conflict often revolves around him feeling like he's not enough, or her frustration that he doesn't take things as seriously as she does. Some fics flip it, though, and have Hermione struggling because Ron's emotional intuition and loyalty are things she can't logic her way into replicating. The emotional core is usually this push-pull between heart and head, with both of them representing one side.
Jealousy plots are huge, obviously, but they're rarely just about Lavender Brown. It's more about Hermione's jealousy of Ron's easy camaraderie with Harry, or Ron's jealousy of Hermione's intellectual connections with, say, Viktor Krum or even Snape. The best fics I've read make their arguments feel raw and real, not just bickering—they're about fundamentally different approaches to life crashing into each other. And after the war, there's so much trauma to unpack separately before they can even think about being together, which is a whole other layer of conflict most post-war fics can't resist.