That, and being able to connect with domain experts as potential co-founders. I've got several very good ideas but they're in industries where I have no experience.
I have a rare combination of deep tech and domain knowledge in a couple cases but... maybe some day...
How do you know they are very good?
Because for most of them, I'm a potential customer and they solve a very unfulfilled need that I know I and many others have. Like, I'm very familiar with the industries as a consumer, but nothing beyond that.