Sin is a hydra-headed problem. It cuts across races, genders and age groups. Sin rears its ugly head in different dimensions. It can be committed against close relations and even outsiders. It has no bounds, hence the need for forgiveness. If sin is not forgiven, humanity is heading for total destruction.
For instance, Jesus died precariously to cleanse the sins of humanity. Very essential indeed, because if the sins of the world were not forgiven, man would be totally destroyed.
Though sin is very painful to whom it is meted out to, but forgiveness has to come in for peaceful co-existence and mutual benefits.
Despite the inhuman treatment meted out to master (Jesus Christ), he still forgave his persecutors in Luke 23:34 showing the importance of forgiveness of sin.
Sin is a very bitter experience but we should try as much as possible to forgive because it is very necessary we do so.