Product's built based on brainstorming: NEVER worked.
Product built around solution to actual problems I've experienced: Always worked, BUT may not have a large enough TAM.
The best way to actually find problems to solve is to replicate something else (as a learning process to actually find the real product you need to build), or talk to people who have problems: e.g. Try an replicate a product with relatively simple core functionality all the way-end-to-end.
During that process you'll probably discover paint point that aren't addressed by any product.
Example from building: Build some GenAI based app that allows users to upload a video and have it "horrified." There may only be a small market in that, but the framework you build to do it could be productized (or subsets of the problem). A simple to use full stack solution where folks can focus on the image / video generation model prompting fine tuning, and then one-click deploy that model wrapped in a whitelabeled ios app with monetization built-in, etc. <-- sell the shovels.
Example from talking: Lot's of buddies have challenges with bringing AI based coding tools into the organization because most don't support on-prem. Is there an on-prem solution that acts like a DMZ? That is, Cursor team could securely deploy their models to containers running on on-prem hardware (with layers of physical and software security to prevent exfiltration of the model weights), while companies can load their propriety data into another container. Win-win.