Fellow aspiring solo founder here! Here are a few books/resources I've found helpful: --- The Mom Test by Rob Fitzpatrick This book stresses the idea of starting with customer interviews before you build anything and how to ask questions of prospective customers to get meaningful information when people's bias is to just tell you, "Yeah, that sounds like a good idea," even though they'd never pay money for it. I spen…
For more of the same, I got a lot out of Lean Customer Development by Cindy Alvarez. Here's a talk from Cindy if you'd like to get to learn more before committing to a book: https://www.youtube.com/watch?v=d5hc7sseHbE