I was involved in several entrepreneur groups in Shanghai when I was based in China -- it seems everyone and his brother was moving there to start a company! -- and had one friend who spent years working on his business plan.
He was in a MasterMind group with me, and each time we met, he had made his business plan more ambitious.
Every time, our advice was: Find your first customer. Do what your customer wants you to do.
His was the kind of business that you could grow, one customer at a time, with no start-up cash.
Instead, he kept redesigning his business plan so it would need more and more investment capital.
I've sat in on VC pitch meetings. VCs know that all numbers and projections in a business plan are imaginary. What they look at is who the founding team is, what their track record is like, do they have the industry contracts to do the sales, to make the products, to run a startup on their own?
My friend didn't have any of those things, just ideas. And while I've heard of people getting funded on just an idea, it is super, super rare.