" If we look at the force of anger, we can, in fact, discover many positive aspects in it. Anger is not a passive, complacent state. It has incredible energy. Anger can impel us to let go of ways we may be inappropriately defined by the needs of others; it can teach us to say no. In this way it also serves our integrity, because anger can motivate us to turn from the demands of the outer world to the nascent voice of our inner world. It is a way to set boundaries and to challenge injustice at every level. Anger will not take things for granted or simply accept them mindlessly.
Anger also has the ability to cut through surface appearances; it does not just stay on a superficial level. It is very critical; it is very demanding. Anger has the power to pierce through the obvious to things that are more hidden. This is why anger may be transmuted to wisdom. By nature, anger has characteristics in common with wisdom.
Nevertheless, the unskillful aspects of anger are immense, and they far outweigh the positive aspects. "

― Sharon Salzberg , Lovingkindness: The Revolutionary Art of Happiness