How many iterations does it take to build a product/service customers WANT?

I've tested many ideas, but none successful. I'm beginning to wonder whether it's not the idea that matters, as much as how far you continue to refine and iterate on the idea.

My process: come up with an idea. Seems decent. Test it out internally a bit, and then I see a bunch of holes for why it wouldn't work. And then I talk myself out of iterating further.

Wanted to ask the community how many iterations of improvements your product needed until you started thinking 'hmm, this could actually work!' or was it instant?

Thanks!