Whenever people live together, they bump up against each other. So part of what makes life possible for humans is the ability for forgiveness. It's the one free act as human beings we can do.
Life is irreversible.
What happens, you can't take back. I can apologize if I'm sincere about it. I can say I'm sorry, but ultimately we put this thing back together when you forgive me. Second, life is unpredictable. You don't know what's going to happen in the next minute, and in the face of that unpredictability, we as a community cannot live together because we just don't know what's going to happen.