What if the idea doesn't really matter? You need to start the journey and be ready to adapt along the way. I've been at it for 12 years now as a cofounder and you'll need to change your product every couple of years. Remember - even Microsoft is shipping Linux these days.
If you're trying to sell and earn money, you don't need an idea, you need customers. From customers to idea is much easier than from idea to customers.
I'm not saying that getting/finding customers is easy neither...
That's the minimum viable product thing - you need to figure out what's actually helpful to people.
For instance, I hope some day someone takes up the mantle and goes out making a decent free identity system. I think most of the North European countries have one of those, and they are all proprietary and suck with no interoperability. If think there's government or even EU money to be had for something that works.
So basically, every citizen needs a way of authenticating, e.g. to submit tax information, log in to banks etc.
