Why Is Forgiveness So Hard Yet So Powerful?

Why do people find it so hard to forgive others, even when holding onto anger only causes pain? Is forgiveness about letting the other person off the hook, or is it more about freeing ourselves from negative emotions? Why does the human heart struggle between justice and compassion? Could pride, ego, or fear of being hurt again make forgiveness more difficult? Why do some people forgive easily while others hold grudges for years? And if forgiveness is so healing, how can we truly practice it without feeling weak or vulnerable?