Our emotions are hardwired physical responses that occur in our bodies, and how we react to certain emotions is also hardwired. Every emotion has an "urge to act" that goes with it. When we feel afraid or anxious, we avoid things. When we are depressed or sad, we withdraw. When we are angry, we want to lash out or yell.

Unfortunately, each of these mood-dependent behaviors serves to increase an emotion, not decrease it. When we feel blue, we think we will feel better if we just withdraw and avoid social contact—but if you've ever tried it, you know that will just makes you feel worse.
When we do the opposite of what our emotions urge, we can start to decrease that emotion. If you are angry with someone and yell and scream at them, the situation rarely gets better and your anger level actually increases. If instead you gently avoid the person until you can solve the situation and then address it at a later time, things are likely to get better and your anger will subside.

If you feel depressed and want to stay in, eat chocolate and watch a sappy movie, doing the opposite could mean going out with your friends. However, you won't alter your mood if you go out but sulk the whole time. You have to throw yourself fully into it and try to act your way into feeling a bit less depressed. That's right—you have to fake it till you make it!

In general, the goal of acting opposite is to decrease the number of mood-dependent behaviors we are engaging in. Rather than letting our emotions determine what we do, we should take control and choose mood-independent behaviors instead!