Baptized Christians are our brothers and sisters, whether or not we realize this. If they commit a sin against us, we must forgive and correct them, "but keep it between the two" of us (Mt 18:15). Lamentably, although this first step in reconciliation works most of the time, it is not done very often.
Notice this command applies to brothers and sisters in Christ, not to unbaptized people. We must forgive, pray for (1 Jn 5:16), and evangelize the unbaptized, but we may not always be called to correct them.
Furthermore, we are to correct our brothers and sisters when they sin, not when we feel hurt because we have judged their motives or taken offense. We should overlook faults, weaknesses, and shortcomings but forgive sins.
Finally, we must never mention (even to our spouses) that a brother or sister has sinned against us. If we have sinned by gossiping, we must repent.
If we obey Matthew 18:15, wars will be prevented, marriages reconciled, families restored, and peace established. Obeying this one verse will change the world. Do Matthew 18:15.