Anger is a natural and mostly automatic response to pain of one form or another (physical or emotional). Anger can occur when people don't feel well, feel rejected, feel threatened, or experience some loss. The type of pain does not matter; the important thing is that the pain experienced is unpleasant. Because anger never occurs in isolation but rather is necessarily preceded by pain feelings, it is often characterized as a 'secondhand' emotion.
Pain alone is not enough to cause anger. Anger occurs when pain is combined with some anger-triggering thought. Thoughts that can trigger anger include personal assessments, assumptions, evaluations, or interpretations of situations that makes people think that someone else is attempting (consciously or not) to hurt them. In this sense, anger is a social emotion; You always have a target that your anger is directed against (even if that target is yourself). Feelings of pain, combined with anger-triggering thoughts motivate you to take action, face threats and defend yourself by striking out against the target you think is causing you pain.
A Substitute Emotion
Anger can also be a substitute emotion. By this we mean that sometimes people make themselves angry so that they don't have to feel pain. People change their feelings of pain into anger because it feels better to be angry than it does to be in pain. This changing of pain into anger may be done consciously or unconsciously.
Being angry rather than simply in pain has a number of advantages, primarily among them distraction. People in pain generally think about their pain. However, angry people think about harming those who have caused pain. Part of the transmutation of pain into anger involves an attention shift - from self-focus to other-focus. Anger thus temporarily protects people from having to recognize and deal with their painful real feelings; you get to worry about getting back at the people you're angry with instead. Making yourself angry can help you to hide the reality that you find a situation frightening or that you feel vulnerable.
In addition to providing a good smoke screen for feelings of vulnerability, becoming angry also creates a feeling of righteousness, power and moral superiority that is not present when someone is merely in pain. When you are angry, you are angry with cause. "The people who have hurt me are wrong - they should be punished" is the common refrain. It is very rare that someone will get angry with someone they do not think has harmed them in some significant fashion.
The definition of whether someone's anger is a problem often turns on whether or not other people agree with them that their anger, and the actions they take in the name of their anger, is justified. Angry people most always feel that their anger is justified. However, other people don't always agree. The social judgment of anger creates real consequences for the angry person. An angry person may feel justified in committing an angry, aggressive action, but if a judge or jury of peers do not see it that way, that angry person may still go to jail. If a boss doesn't agree that anger expressed towards a customer is justified, a job may still be lost. If a spouse doesn't agree that anger was justified, a marriage may have problems.
Whether justified or unjustified, the seductive feeling of righteousness associated with anger offers a powerful temporary boost to self-esteem. It is more satisfying to feel angry than to acknowledge the painful feelings associated with vulnerability. You can use anger to convert feelings of vulnerability and helplessness into feelings of control and power. Some people develop an unconscious habit of transforming almost all of their vulnerable feelings into anger so they can avoid having to deal with them. The problem becomes that even when anger distracts you from the fact that you feel vulnerable, you still at some level feel vulnerable. Anger cannot make pain disappear - it only distracts you from it. Anger generally does not resolve or address the problems that made you feel fearful or vulnerable in the first place, and it can create new problems, including social and health issues.