I look for a "social friction" moat. If an idea can be executed entirely from behind a keyboard, the competition is infinite. But if it requires me to sweat, do meatspace socializing, and actually walk into a physical building to hand people a solution, competition drops to near zero.

The literal application of "do things that don't scale."

Beyond that, I look for ROI besides wealth. Even if it doesn't blow up in popularity will it still improve my life if just a few adopt it/appreciate it?