It's clear from this story that two things happened in that boy's life. You see, forgiveness is not overlooking or allowing or putting up with inappropriate, cruel, or hurtful behavior. Forgiveness is not about accepting sin. Sin is sin, and should be as hateful to us as it is to God. Forgiveness is about telling someone whose behavior is wrong, and then helping them move beyond the wrongness into appropriate, civil, or loving behavior.
Forgiveness is about overcoming sin.
Jospeh and Jesus also tell us that forgiveness is about overcoming revenge. Revenge never solves a problem, and rarely feels satisfactory. Usually revenge leads to more revenge, and a whole cycle of sin is repeated. Forgiveness is as much about overcoming the desire for revenge as it is about overcoming wrongful behavior. Joseph and Jesus both knew the power of forgiveness to change lives.