Forgiveness is a Heavy Burden
We have each been insulted or hurt or betrayed by someone in our lives at some point. To carry the anger, disappointment, bitterness or overall poison for the offending person is simply a way to relive the pain over and over again - which seems pretty pointless and self destructive. This is why each religion teaches the importance of forgiveness.
With forgiveness we might include compassion. The ability to understand what the other person's perspective or world view which could lead to not taking the actions that occurred personally.
As we walk down the path of compassion we might stumble across empathy when we realize, "oh shoot, I have acted the same way once or twice, or multiple times in my past." Or we might even get to realize that the way the person was responding to us was simply a reaction to what we were doing to them.
With that we start to carry the burden of responsibility. At this point we are at a crossroads of where to "lay blame." Of course blame only will lead to the need to go through the forgiveness cycle again, which becomes an endless cycle of Hell.
To break out of the cycle we can choose to let things be in the past and move on. But then we have to come to terms with breaking away from a relationship or learning to trust the other person, and ourselves with that person again.
Which is the lesser burden? Which decision can we live with long term? To walk away seems quick and easy, but the memories and "what ifs" linger. To stay means to rebuild, slowly and carefully, hoping not to screw up again.
When you consider the burden of forgiveness, it starts to be easier to understand why so many people choose to hold a grudge.

