The mind is everything. It all boils down to how you see yourself, and your thought patterns.
Think negatively, and your world will be negative. Think positively, and your world will be positive.
I don't hold grudges against people. I don't hate anyone. It's rare for me to hate anyone. I forgive people so that I can have my own peace. For me, peace of mind is key. We have a limited time on this planet. A very short time, at that. Why waste your time getting angry. Why waste your time moping over some sh1t that you know is trivial, or very unimportant? The more you get upset, the longer your give up your peace. And I don't think you should surrender your peace for ANYTHING.
I look into meditation and having a peace of mind. When my mind is still and silent, all answers in my life come to me. I'm at peace; I can move through out the day without being disturbed by outside circumstances.
However, when my mind is running a thousand thoughts a day, I'm angry, I'm sad, I'm annoyed, I let all types of trivial things in life get to me, even the smallest things.
It's like training your muscles/body. You have to TRAIN the mind to be a certain way. It takes time. It's nothing that happens over a couple minutes. It's like a muscle that has to be built.