When you say something outloud, you want to believe it. And of the class, of "things you want to believe" how many of those are true? If they are true then they are self evident and need not vocalization. But by saying something out loud, it shows your need to reinforce belief in its truth. Why do you need that reinforcement? Because your belief is unstable? Are you insecure in allowing others to have differing beliefs. Do you feel it cuts into your foundation? You want to will it into truth? Sometimes this works. If an outside person agrees then it becomes truth. However, it becomes and remains their truth but is only yours for a moment. External support is fleeting. I'm not sure if this is true but I'd like to think that it is. It would make psychiatric diagnostics much easier.