There is a weird psychological barrier that is crossed when you say something out loud.
When you're really ashamed of something, speaking it to another person does an amazing thing. Somehow by saying it, by articulating these thoughts into vocalic and consonantal sounds that form into psychosocial symbols of greater realities, it changes things. It gets the darkness out of the insides and into the light, where you can be a little more distanced, a little more safe from it, with a little more perspective.
On the other hand, if there's a dangerous thought floating around in your mind, sometimes saying it out loud can be the worst thing ever. The words coming out of your mouth gives shape to that danger and makes it real. Reciprocal influence? You shaping your words and your words shaping you.