You mentioned that people might be applying frameworks in retrospect to justify luck. There’s definitely truth in that, but the "framework" that actually works is narrowing the information gap between you and the user.

Instead of trying to find a "niche" like accounting for plumbers from thin air, go to where the "plumbers" (or whoever your target is) are actually venting. Reddit is a goldmine for this because people are surprisingly honest when they are frustrated.

I’ve found that spending two weeks just reading subreddits related to a specific industry—and looking for the most upvoted "pain" posts—is worth more than six months of SEO and "calibrating" a product no one asked for. The goal is to find a problem that is currently being solved badly. If you build the "not-bad" version of that solution, you don't need a massive marketing budget; you just need to show up where the complaining is happening.