The way I've always read it, the book's central thrust isn't really just about men being mad at the modern world, though that's the shiny wrapper it comes in. It's more about the deep, corrosive need for meaning and the violent, self-destructive forms that search can take when all the old structures—jobs, possessions, identity—feel like a cage. The Narrator creates Tyler not because he's bored, but because he's so utterly empty that he has to invent a new, more 'real' person to feel alive.
What gets me every time is how the book dismantles its own rebellion. Project Mayhem ends up just another rigid hierarchy with its own rules and uniforms, swapping one form of consumerism for another. The final twist, with the Narrator shooting himself to 'kill' Tyler, forces you to question if any of the chaos actually solved his original emptiness or just gave it a louder, more destructive voice. The book feels like a trap that shows you the prison, offers you a way to smash the walls, and then reveals the sledgehammer you're using was made by the warden all along.
I think the theme that lingers isn't a lesson, but a chilling question: when you reject everything you're supposed to be, what's left to build with, and are you even capable of building something that isn't just another kind of ruin?