You don't have to do this of course if your price point is $10,000+, you could go get agreement in principles if it's a bigger product.

But for smaller products that are online only signup? Getting all dewey eyed over someone not getting their $10 p/m new to-do app, and go spend months building it instead and then finding there's no market?

You're making the wrong call there. Test the market, prove you can sell it, then make it. A couple of people not getting their $10 p/m app vs you losing $10,000s on wasted time is worth that.

To be honest, as a professor what have you ever had to do business-wise? You've never left academia apparantly. It must be nice to critize but I have no respect for your advice.