Story
I've had hundreds of would-be entrepreneurs contact me with great news: They have the next big thing, but they can't risk telling me (or anyone else) about it until I sign some form of idea insurance, usually a nondisclosure agreement (NDA). Like every other sensible investor on the planet, I decline the request to sign the NDA, forgoing the idea, often to the shock, awe, and dismay of the stunned entrepreneur.
Why do I avoid this conversation? Because entrepreneurs who behave this way clearly overvalue ideas and therefore, almost by definition, undervalue execution. Brainstorming is a risk-free, carefree activity. Entrepreneurship in the literal sense of “undertaking” is not. Strap on your seat belt if you're signing up for a startup. It's a high-velocity experience.
If you have a brilliant idea, it's safe to assume that a few very smart people are working on the same thing, or working on a different approach to solving the same problem. Just look at the number of different travel apps on your iPhone or the number of diet and exercise sites on the Web for an example of this.
Almost anyone can (and has!) come up with a great idea, but only a skilled entrepreneur can execute it. Skilled in this case doesn't mean experienced; it means flexible and action-oriented, someone who recognises that mistakes can often be corrected, but time lost postponing a decision is lost forever. Ideas, however necessary, are not sufficient. They are just an entry ticket to play the game.
Moral of the story
If you overvalue your ideas you undervalue execution
Brainstorming is a risk-free activity, entrepreneurship and building things is not
Mistakes can often be corrected, time lost postponing a decision is lost forever