When you have to convince a lot of different people of a thing, you end up convincing yourself.

This can't happen if the idea actually isn't any good. But if you have good answers to all of the questions and concerns you get, you get more convinced of it.

By being forced to explain it in ways that lots of people get, you create a resilient understanding.

The "I haven't found a question I can't answer" can be a credible signal that the idea actually is good. But there are two things that can make this a less trustworthy signal:

1) When you know the idea 10x better than anyone else will, so you get superficial questions you can overwhelm them with forethought on; not that you're right, just that you've thought about it more than they're able to in the moment.

2) When your ego is tied to the thing; if it fails, then you fail. You will do the kayfabe of disconfirming evidence but no more.