It’s not uncommon to see especially new writers confuse structure and formula. Proudly planting their flags as artists, they refuse to be limited by the supposed stamped rigidity of formulaic structure. But that’s the problem: they confuse the adjective for the noun.
Structure isn’t formula. Just because every house needs a foundation, support walls, a bathroom, kitchen, etc., doesn’t mean those have to be executed according to the same plan in every house. That’s what would make them formulaic.
Ditto structure and story. Rising tension or conflict requiring some kind of resolution in the end; the action or event that initially creates that tension; scenes that contribute to that rising tension—those are as definitive to story as the structural components of a house. If you don’t have them, you won’t have a readable story anymore than a house without walls or bedrooms or a roof is a livable house. Certain ingredients are simply necessary.
What makes them formulaic is applying them in a set, routine fashion—running them through the same formula—regardless of the nature of the story. If you’re thinking in terms of page numbers for various plot points (inciting incident by page X, turning points by page Y) and/or supposedly necessary steps (mentor arriving here, refusing the call there)—that’s formula. That’s beguiling for new writers because, well, it’s easier than the real exploration of their story ideas that it often replaces. Rather than finding the structure that best suits the individual needs of their particular story, they begin immediately fitting their ideas to a preconceived, generic story structure, derived from the retroactive analysis of scores of stories across multiple genres with little to nothing in common to theirs. Only they’re surprised, though, when their story seems bland and reminiscent of so many others.
Formula confuses common for necessary. You can find elements (as well as when they occur) that are common to many stories, but aren’t elemental to all stories. All effective story requires a certain structure, but that structure doesn’t have to be formulaic. Recognizing the difference is the difference between dressing your story like a drunk pirate or a reform school student. Who would you rather follow for two hours?