Although they are often unpleasant, negative emotions have an important purpose in our lives, because they prepare us to deal with potential threats. If someone transgresses against you, you become angry, so that you might retaliate and discourage future transgressions. If you find yourself in a dangerous situation, anxiety will help you avoid the same situation in the future. The purpose of negative emotions is to focus your attention, make you aware of things that are very important, and get you to take appropriate action. In a way, they are safety mechanisms – your mind thinks you’re in trouble and cuts off access to other states to make you react more quickly.
In this sense, there are no ‘negative’ emotions. As an example, eyewitnesses to a violent attack can often describe the weapon used in detail, but remember little about what the assailant looked like. When there’s a dangerous maniac around, you need to know that he’s carrying a knife, and where exactly that knife is at all times; not whether he matched his shoes with his belt that day. The problem of course, is that in some people, these unpleasant emotions are triggered too often, or in situations where they aren’t needed.
On the other hand, positive emotions have the opposite effect. Rather than narrowing our attention and potential behaviours, they broaden it. Instead of reducing the number of thoughts that enter your head, or the restricting your behaviours, these repertoires are increased. So when your happier, you’re more creative, flexible and you look at the bigger picture rather than the little details. This makes uplifting moods more useful for tasks like brainstorming, where you have to come up with new ideas. It also makes them less effective for tasks like proofreading, where attention to detail is essential. By understanding how our mood influences our perceptions, we can make sure our emotions are appropriate for the task at hand (such as through our choice of background music; something upbeat for creative tasks, and something more downbeat and thoughtful for tasks that need attention to detail).
Fredrickson, B. L. (2001). The Role of Positive Emotions in Positive Psychology. American Psychologist. 56 (3), 218-226.