Thoughts and feelings form a reciprocal relationship; emotions generate thoughts and thoughts trigger emotions. Therefore, thinking negatively generates a spiral into negative emotion and more negative thoughts.
It follows that negative emotion can be reinforced by negative thought or changed by positive thought. For example, thinking, “I can’t do that because of my Parkinson’s (or my stammer)” generates a negative emotion, which supports the negative thought. On the other hand, thinking, “I will give it a go” creates a positive feeling. This reforming of emotion by thought gives us the opportunity to steer ourselves through rough, negative seas until we reach calmer waters.