Forgiveness is one of the most important aspects in life. It appears to be the toughest, and many people say that it's illogical or impractical, however, let's first understand what forgiveness is all about.
Someone did something to you in the past that caused you pain - may be a week ago, a month ago, or ten years ago. This could be financial loss, a betrayal in relationship, carelessness, a sexual abuse, or simply an emotional torture. Yes, it was wrong, and bad, and unacceptable. Let's not talk about it for a while now. It's time to realize how you have affected yourself by continuously remembering and re-living that incident in your mind. That person did it once, on that day, that date. However, how many times have you done it to yourself? Ten? Fifty? Or even more?
It is important to realize how much we dwell on our past (especially the negative past), and simply forget that we have the power now to create the life we desire. I can understand that incidents such as those do affect one's emotional stability, one's happiness. In fact, sometimes such incidents also happen to change the course of our lives, and take life in a direction that we'd never even thought of. However, now that you are coming to an understanding of the fact that you are energy, powerful energy, able to create anything that you desire in life, it would be important to clean-up the mind of all the unnecessary baggage.
Even if, let's say, you've just heard about the 'law of attraction' or you've just heard the statement 'thoughts create things', and may not have still experienced the working of the law of attraction in your life, so, you don't believe completely in the law of attraction, forget about all of these concepts for a little while. Do you want to be happy NOW? Do you want to live the life that you've always dreamed of? Do you want to take little steps (if not big ones) towards the direction in which you want to take your life now? Do you want to trust that when you slightly change the way you look at life or this world, your life experience changes? If your answer is Yes to those questions, you must develop your mind and forgive.
Make a list of all your achievements in life. Take a bird's eye view of your life and enlist all the things you're proud of. Make a list of all the wonderful and amazing things that have happened in your life so far. This will help you realize how beautiful your life is, and empower you enough to make you realize your own potential. As you gradually shift your focus towards the good things in life for a consistent period of a week or two, you will start realizing the benefit of forgiveness (even though it looks unrelated right now). Although I would not encourage you to remember that situation anymore, I'm sure you will now realize that you did have some traits within you that you now feel the need to change.
Holding grudges or resentment in your mind keeps you trapped in the cages of your own mind, which (let's understand first) is not a cage at all. The mind is not a cage. We often end up turning it into a cage by blocking ourselves by the virtue of our own thoughts. In fact, holding negativity in the mind for a prolonged period of time manifests into undesired physical illnesses.
Often, you may naturally want the other person to be punished by God or by the law or by someone, and that (you may say) is the least thing to expect now. Yes, that's perfectly fine, but since you have no control over that person's life anyway, why wait!? Why do you want to wait for that person to suffer before you come out from your suffering. He may suffer, he may come back to you some day asking for forgiveness, he may regret his actions badly, or even not. Yes, this may not sound good to the ears now, but remember, if the laws of energy works for you, it works for him too. He will receive what is within his Thoughts / Mind (just as you did via him). However, it would be good if you take care of what's within your mind / thoughts, and now understand your own "power to create", and move in the direction of what you now want in life.
Later as you realize how you create your own life by the virtue of your thoughts and the law of attraction, you will realize that there is no need to forgive anybody, because they were not "wrong" in the first place. This is deep and needs deep introspection and understanding of this spiritual knowledge. You will reach a stage in your life, when you won't even feel like condemning the other person for his so-called "wrong doings".
Remember, financial loss can be turned into profit with persistent efforts, one loss in relationship doesn't mean you can't live the most wonderful relationship in the future, one who abused your body cannot abuse your mind (it's only you who abuses and tortures your own mind by negative thinking), and nobody can penetrate your mind and change your thoughts. You are that mind, and you have 100% complete control over it.