I had 4 failed attempts to monetize side projects, before finally stumbling upon something that doesn't need marketing at all. However, it does require competin

I had 4 failed attempts to monetize side projects, before finally stumbling upon something that doesn't need marketing at all. However, it does require competing at the absolute top level, all the time. What's the catch? You find these things almost exclusively in zero sum games. But since we are talking money here, as a solo dev I pick this over marketing, every single time.