Do you know solopreneurs who succeeded solving someone else’s problem?

I’m a software engineer and the problems I experience are usually already solved by other developers.

I decided to research other industries and right now validating an idea of a product for HRs.

My marketing mentor said it’s gonna be hard because I don’t have network and experience in that field. Plus it’s pretty competitive.

Do you know any solo founders who built something in completely different industry from theirs and succeeded?

P.S. I’m gonna validate my idea anyway. If I have to fail with it, I’m gonna fail fast and move to the next idea.