You will notice that when you smile at someone, the "imitation response" that neuroscientists have discovered prompts a natural tendency for the other person to smile back. This phenomenon indicates that the face is an enormously rich source of information about emotion. In fact, our face is not just a signal of what is going on in our mind; in a certain sense, it IS what is going on in our mind.
The expression on our face is sufficient to create a marked change in the autonomic nervous system. You can prove this to yourself by thinking of a sad thought. With that thought still in your mind, look up at the ceiling and smile. Then try to keep that sad thought.
We think of the face as the residue of emotion. But the process works in the opposite direction as well. Emotion can START in the face. The face is not just a secondary billboard for our internal feelings. It is an equal partner in the emotional process.
Little did I realize when I wrote the opening few sentences in my book that my statements would be scientifically proven. The first few lines are: "Life is a conversation. Interestingly, the most influential person we talk with all day is ourself, and what we tell ourself has a direct bearing on our behavior, our performance, and our influence on others. In fact, a good case can be made that our self-talk creates our reality."
Our self-talk becomes our thoughts and shows on the expressions of our face.
Scientists are discovering that the face is governed by a separate, involuntary system. Whenever we experience a basic emotion, that emotion is automatically expressed by the muscles of the face. Our involuntary expressive system is the way we have been equipped by evolution to signal our feelings. The argument can be made that the system evolved so that parents would be able to take care of their children whose feelings are shown on the face.
We have no switch to turn our expressions on or off, and this may be a good thing. Since others can see what you feel, and since people do better when they feel better, and since others may involuntarily imitate your responses, having positive self-talk increases your effectiveness.