What do you mean by "a great idea"? An idea that your friend and many others would enjoy, or a monetizable idea that can become a sustainable business? If you

What do you mean by "a great idea"? An idea that your friend and many others would enjoy, or a monetizable idea that can become a sustainable business? If you have an idea ready for execution that you deeply believe can be a profitable business, what's the downside of executing? The fact that you are not the customer shouldn't be a showstopper. But, you should be close enough to the customers to understand their needs, and what they would pay for.