Acting on the urge an emotion brings can strengthen that emotion. Acting opposite of the urge can lead to opposite emotions.
When you have a feeling, that feeling gives you an URGE, a desire to act in a certain way. Sadness makes you want to shut down. Fear (anxiety) makes you want to avoid and run away. Anger makes you want to attack something or somebody. Shame makes you want to hide. Disgust makes you want to get away from that thing that disgusts you.
The more you act on the URGE that an emotion brings, you actually strengthen that emotion, making it more likely that you will continue to feel that feeling and that you will feel it even stronger.
There is a skill called OPPOSITE ACTION that basically says “do the opposite of what your feelings make you want to do”. By doing this, you can stop the same old feelings from getting stronger and more frequent. In fact, you can start generating OPPOSITE feelings (like joy, peace, contentment, love, happiness, confidence) by doing OPPOSITE actions. That is, actions that are the OPPOSITE of what the URGE makes you want to do.
So if I’m sad and I have an URGE to shut down, I can do the opposite by making myself get busy, call someone, or go for a walk. And it will help me feel less sad and more happy.