"Forgive others because it is good for you." That is not the gospel. It has the sound of the gospel, but it is not the gospel. It translates the power of forgiveness into a respectable language of psychology, but the translation is unfaithful. We are not reading the same story.
It is true that forgiveness benefits the forgiver. There is some psychological release. But this reduces forgiveness into a subjective experience. It forgets, maybe even denies, the objective reality of forgiveness and all the other elements pertaining to forgiveness, God, sin, judgment, and grace. It even twists what is supposed to be the most altruistic act into a selfish act. And to that extent, has one forgiven the other when his main motive is to move on with his life with no care for the one he has supposedly forgiven?
Did Jesus forgive so he can die without anger? Did Stephen pray "don't hold this sin against them" so he can meet Christ with a good conscience. They forgive as their last act before their death because sin and judgment was real and their compassion did not want the judgment of God to fall upon their murderers.
The gospel is that the judgment of God has truly passed over us because Christ has paid for our sins and his forgiveness accomplishes a real change of our relationship with God. Even more, we are given that same power and charge. The resurrected Jesus meets the disciples and, breathed on them and said, "Receive the Holy Spirit. If you forgive anyone his sins, they are forgiven; if you do not forgive them, they are not forgiven." - John 20:22-23
Our prayer gives a another chance to those who sinned against us, or imprisons them in damnation. That is awesome power. With that power, comes great responsibility. The one who knows such power and has experienced forgiveness will always seek opportunities to share the good news of forgiveness and practice it himself.
When Stephen prays forgiveness for his stoners, the stoners hurl their stones with more vehemence. Saul, a young teen at that time, stands in judgment and laughs at the pardon he does not need. In fact, Stephen's prayers has only strengthened his animosity against Christ-followers. The First Persecution is, in many ways, a conflagration lit by Saul's anger. Where many of the priests were scared to imprison the apostles, Saul did not fear the unpredictable crowd or Pilate who could takes such religious persecution as overstepping of boundaries. Saul's anger was agitated by Stephen's prayer. There was no subjective change anywhere in the story. But there was an objective change. Christ did not hold the murder of Stephen against Saul. Christ upheld his promise that if his follower forgives, He too will forgive. So when Saul is galloping down to Damascus, Christ knocks him off his horse and gives him a second chance.
So forgive that person (you fill in the name). You will launch him/her into the grace of God.