Why is forgiveness important? Because it's good for us, whether it's forgiving someone else or yourself. But adopting a systems perspective around a wrongdoing is a big shift for anyone. The more intense the situation, the harder it can be. (Before you continue, please note that extreme events can be very hard for individuals to put into a systems perspective. A systems perspective can involve a long time frame and societal level processes preceding the event that affects an individual. A systems perspective doesn't ask why or if something is fair.)
Triangles are mechanisms to deal with the tension or discomfort that will inevitably arise in a two-person relationship. This is because the majority of individuals are not highly differentiated. We have a level of immaturity that leads to tension in our relationships. This often shows up as the tension and discomfort that arises when people disagree. We perceive the disagreement as a threat to ourselves and or the relationship (which is also a threat to ourselves).