I always tell my kids, there's a difference between understanding the influences on your behavior and forgiving the choices you make. You had a bad day and you didn't sleep well and your sister was annoying you? Yeah I understand why you were upset, but that doesn't make it OK to hit her.
Understanding and forgiving are different, and forgiveness comes when you're sorry and try to do better. If you're trying to justify your bad decision, it's like you're asking for an excuse to do it again next time.