Consistently happy people are either in one of two conditions. Either no one has ever wronged or slighted them in any way. Or else they have forgiven those who have. Since it is almost impossible not to have been wronged or slighted, if you want to master happiness, you need to learn how to forgive.
Forgiving is like floating on water. You don't need to do anything. You just need to let go. When you were a young child of five or six, you became angry at your brothers, sisters, friends, and classmates. You might have even said, "I won't forgive you." Now when you look back at the vast majority of those situations, you will see that they were trivial. It is at present easy for you to forgive someone for not giving you a bite of their ice cream, not letting you play with their toys, or grabbing your ice cream or toys. Just as you have already forgiven them, you will be able to forgive others for more recent events when you realize that most things are trivial when compared to your emotional and spiritual well-being.
We all need our Creator's forgiveness. By forgiving others we elevate ourselves and render ourselves more worthy of being forgiven. When you find it difficult to forgive, pray with your own words for the strength to forgive
(From Rabbi Pliskin's "Happiness",p.171)