Ideas... We all have them, day in day out. If I could sell 1% of my ideas, I'd be rich, just by the sheer volume of idea I have. Point is, nobody would pay for an idea, because without acting upon an idea, an idea in my head just stays... well, an idea in my head. Nobody will ever know if it was a good idea or a bad idea.
This is exactly the dilemma startups face: how do we know if an idea is worth something? Is this idea so good that we can build a company on top of it?