Anger will never disappear so long as thoughts of resentment are cherished in the mind. Anger will disappear just as soon as thoughts of resentment are forgotten.
Resentment is a common enough emotion, it seems more evident today than when I was younger. Resentment can never be positive; it always has a destructive end, since resentment is focused on the self and the need to voice sentiments of perceived wrongs and injustices. It tends to become a way of life. Self-entitlement often feeds resentment; so does a myopic focus on the needs of the Self. Resentment rarely if ever looks at the needs of others, although in some cases it can appear that way.
I would expect that a majority of criminals behind bars are resentful and loudly claim innocence. I would also say that a majority of criminals hold many resentments against society. Not all resentful individuals are criminals, of course, but many criminals are resentful in some form or fashion, notably ones who take from others what is not legally theirs. Thus generally explains their actions against society. Resentment often turns to anger, if it is long-lasting and expectations are unmet.
There are psychological explanations for resentment. In a Psychology Today blog posting ("Overcoming Chronic Resentment and the Abuses It Causes"; Aug 15, 2011), Steven Stosny writes:
Unlike anger, which is stimulated by discreet incidents or thoughts, chronic resentment is a general ego defense - the more fragile the ego, the more resentment required for defense. For those most in need, ego-defense is more important than learning, truth, and reason. Hence resentment greatly distorts thinking - through oversimplification, confirmation bias, inability to grasp other perspectives, and impaired reality-testing (inability to distinguish thoughts from reality). Over time, resentment becomes a world view or way of life.Resentful individuals nurse and feed their resentments, bolstered by self-entitlement and a society that has made the Individual self-important. What good does that do? Nothing that I can think of, yet it persists. People (and groups) who are highly resentful share a few common character traits, including never having an ability to empathize, displaying a lack of social awareness, having a hard time admitting wrong, lacking respect for authority and making excuses for wrong, unethical or immoral actions.
You will note a pattern in this list—these are all traits that are counterproductive to establishing long-lasting and genuine relationships; they are also traits that go against the best interests of a well-functioning civil society. Resentful people (and groups) rarely build, but they are highly adept at destroying.
Now, I have met my share of deeply resentful individuals, some who are familial relations, some who were once considered friends, and others who were colleagues at work. Since I like to enjoy life—and I have every good reason today to enjoy it more—I tend to avoid individuals who have made resentment part of who they are. There is nothing good in the encounter.