Nobody is perfect. Everyone carries their own pain which influences the decisions they make. This does not condone thoughtless, insensitive, disrespectful, selfish, hateful/spiteful/vengeful actions but it does make them easier to understand. Many people are sadly just too stubborn, ashamed, or in denial to admit to any hurt they have caused...
I forgive those who hurt me. I don't do this for their benefit - I do it for my own. I do not want any lingering anger, bitterness, resentment or judgments eating away at me - even at unconscious levels - and I certainly don't want any perceived transgressors to have a hold over me because I chose to harbor rather than release those feelings. I then restore my boundaries and no longer dwell on the offense. Every time I think of those who have hurt me I send them love.
In many cases I've discovered that on some level I directly or indirectly allowed events to happen. If we invite someone into our lives, give them power and they abuse it, aren't we also responsible? If we continue to give them power by seeing ourselves as victims, aren't we responsible for that, too?
If love and compassion lightens us, and anger and resentment weighs us down, which of those benefit us and which does not?
We can choose to be masters of our emotions by giving ourselves, and no one else, the power to affect how we feel. Forgiveness is the most effective tool I've found for achieving that. Forgive those who have hurt you in the past. But more than this, forgive yourself for allowing them to hurt you ;)