Will Wight self-published Unsouled in 2016. The first book in what would become the Cradle series. His protagonist, Lindon, is born with a damaged core in a world where spiritual power determines everything from your social rank to whether your family will feed you. Everyone in Sacred Valley tells him to accept it. He doesn't advance. He doesn't fight. He survives by being clever and careful and deeply, personally afraid.
The series went on to sell millions of copies. Readers stayed up until 3am pushing through Lindon's advancement from Copper to Underlord to Monarch, watching him accumulate techniques and allies and enemies who respected him because they had no other choice. But the thing worth studying isn't that Wight wrote a character who gets stronger. Hundreds of cultivation fantasy novels do that. The thing worth studying is that every time Lindon advanced, it felt like he'd paid for it with something the reader could feel.
That's the line between progression fantasy that works and progression fantasy that reads like a spreadsheet with a plot taped to the front.
If you're writing in this space, if you're building a cultivation system or a tiered magic structure or any world where the protagonist climbs a visible ladder of power, the question that matters most isn't how your system works. It's whether the reader believes the cost.
Making every level-up cost something human
The temptation in progression fantasy is to make advancement feel good. The character trains hard, masters the technique, breaks through. The reader gets the dopamine hit. And that works, for a while. But the books that people recommend to strangers on Reddit aren't the ones where advancement feels good. They're the ones where advancement feels heavy.
In Bryce O'Connor's Iron Prince, Reidon Ward enters a military academy with an adaptive combat implant rated at the lowest possible level. His CAD is a joke. The system itself has told him, in quantifiable terms, that he's weak. When he starts advancing, it's violent and confusing and it costs him relationships with people who'd been comfortable ranking above him. The growth is real, but so is the friction it creates in every direction.
What O'Connor understands, and what's worth sitting with if you're designing your own progression system, is that power changes the social physics of every room your character walks into. The advancement itself is mechanical. The cost is relational. A character who breaks through to a new tier and loses a mentor who can no longer teach them, who watches old friends become wary, who realizes the person they were at the last stage of power wouldn't recognize what they're becoming at this one. That's the kind of cost readers carry with them after they close the book.
The training arc that doesn't bore the reader
Here's the honest problem with training arcs: most of them are boring. A character sits in a cave and meditates for three chapters. They practice a sword form until they get it right. The writer describes the internal sensation of spiritual energy flowing through meridians, and it reads like a yoga manual translated from Mandarin.
John Bierce solved this in Mage Errant by making Hugh's training inseparable from his relationships. Hugh doesn't sit alone and grind. He trains with a small group of misfits, each with a different affinity, each with problems the others don't fully understand. The training sequences work because they're also friendship sequences and they're also character-development sequences. You're never reading about a magic system. You're reading about people figuring things out together, and the magic system is the vocabulary they use to do it.
I'm not entirely sure there's a way to write an interesting training montage in isolation, where it's just one character alone with the system. Maybe someone's pulled it off. But every example I can think of where a training arc held my attention, there were other people in the room, and what the protagonist was really learning was something about themselves they couldn't have seen without the mirror those other people provided.