This practice does two things:
1) Makes you vulnerable. If you say that you are afraid of something, you effectively open yourself up and free yourself to do something important. Say it out loud. It puts the problem into perspective because the words absorb the fear.
2) Validates the idea. It's the last test you should run before you proceed. Say it out loud. Does it still sound like a good idea? Something worth pursuing? Or does it sound crazy and/or awkward?