Unfortunately the reality is that you will almost definitely not have a bulletproof idea from the get go. And even if you do achieve product market fit, you may (read: probably will) lose it after x months/years. Good enough is what you are going for here. And then just ship. My company is currently at tens of millions in revenue and we still don't have a bulletproof, defensible product. But we have the space and time to iterate towards it.