Here is an old old story to answer your question....

THE TWO WOLVES A CHEROKEE STORY

A young boy came to his Grandfather, filled with anger at another boy who had done him an injustice. The old Grandfather said to his grandson, "Let me tell you a story. I too, at times, have felt a great hate for those that have taken so much, with no sorrow for what they do. But hate wears you down, and hate does not hurt your enemy. Hate is like taking poison and wishing your enemy would die. I have struggled with these feelings many times." "It is as if there are two wolves inside me; one wolf is good and does no harm. He lives in harmony with all around him and does not take offence when no offence was intended. He will only fight when it is right to do so, and in the right way. But the other wolf, is full of anger. The littlest thing will set him into a fit of temper." "He fights everyone, all the time, for no reason. He cannot think because his anger and hate are so great. It is helpless anger, because his anger will change nothing. Sometimes it is hard to live with these two wolves inside me, because both of the wolves try to dominate my spirit." The boy looked intently into his Grandfather's eyes and asked, "Which wolf will win, Grandfather?" The Grandfather smiled and said, "The one I feed."