How Do You Know if You Have a Great Idea?

At P&G, you're taught to think in threes. You know the direction you should go. And even stories where within that you overstep authority and something perhaps negative happens, but you still learn a lesson. The key part is figuring out how do I get people to say yes or when you are the ultimate decision maker,. How do you decide if the idea is the right idea or needs further refinement and further shaping?