Before Rainbow Rowell published a single novel, she spent years writing advertising copy during the day and fanfiction at night. Most people skip this part of her biography. They jump straight to Eleanor & Park and the bestseller lists. But the fanfiction years weren't the warmup. They were the training.
When Rowell wrote Fangirl in 2013, she built the entire novel around a college student named Cath who writes Simon Snow fanfiction. Cath isn't dabbling. She's prolific, she has a massive readership, and her fic is better than most of the original fiction being workshopped in her university classes. Rowell wrote Cath that way on purpose. She knew what that world felt like from the inside, knew how seriously fic writers take pacing and voice and continuity, because she'd done the same work herself for years before anyone was paying her for it.
Here's the part that gets interesting. Rowell became so invested in Simon Snow, the fictional character inside her fictional character's fanfiction, that she eventually wrote Carry On, an entire original novel set in that world. Then Wayward Son. Then Any Way the Wind Blows. She turned her character's fanfiction into a real, published trilogy. The skills she'd built writing fic, the instinct for serialization pacing, the ability to keep a reader emotionally committed across hundreds of thousands of words, the ear for how characters sound when they're alone versus when they're performing, all of it transferred directly into her career. She didn't leave fanfiction behind. She brought it with her and built on top of it.
Borrowed characters teach you what your own characters need
There's something specific that happens when you sit down to write a character someone else created. You can't just make them do whatever you want. If you're writing Harry Potter or Katara or Wednesday Addams, the reader already knows how that person talks, what they'd notice walking into a room, how they'd react to being embarrassed. You have to match it. And matching it requires a kind of reverse engineering that most writing workshops never teach.
You end up asking questions you wouldn't think to ask about your own characters. Why does this person use short sentences when they're angry? Why do they deflect with humor instead of going quiet? When you get it right and a reader comments "this sounds exactly like them," you've just proven you understand characterization at a mechanical level. You know what makes a voice consistent.
That skill doesn't disappear when you start building from scratch. You just redirect it. Instead of matching someone else's character, you're maintaining the internal logic of your own. The muscle is the same.
Serialization builds the muscle that outlining can't
Beth Reekles was fifteen years old when she started posting The Kissing Booth on Wattpad. She wrote it chapter by chapter, publishing each one as she finished it, with millions of readers following along in real time. There was no going back. No restructuring act two after she'd figured out the ending. Each chapter went live and stayed live, and the next one had to pick up where it left off.
That book got a traditional publishing deal. Then a Netflix movie. Then two sequels.
The conventional writing advice would say Reekles did everything wrong. She didn't outline. She didn't revise before showing anyone. She wrote in public, with all the mess visible. But what she built in the process was something you can't get from outlining alone: the ability to trust her instincts mid-draft. She learned to write forward, to commit to a scene and let it stand, to end a chapter in a way that made people come back tomorrow.
I'm not sure why serialization trains those instincts as well as it does, but I think it has something to do with the fact that you can't hide. When your chapter is live and readers are responding, you learn very quickly what a dead scene feels like. You learn what momentum is because you can feel it break.