What's your favorite side project you've ever worked on, and why?

So far, i made a an AI chat to help jobseekers prepare for an interview. It would ask them a question, they give a response, then it would give feedback and a score. I had the Ui look like your on a webcam with a bot😆 Ultimately nobody paid, that's when i realised that if i want to make a successful product, build for people who actually have money and are use to spending lol