Forgiveness is necessary

Very simply:
you must forgive others and yourself to be happy.
Not so simple:
this is, how you say, "easier said than done," yes?

Most major religions demand forgiveness.
This comes in 3 parts:
Asking forgiveness of God, the Divine Creator
Forgiving others in likeness of the Divine
and forgiving yourself in turn.

If you do not forgive others, not only does this hurt your relationship with others but this hurts yourself.
Vengeance is a meal best served cold and excellent when not served at all.
Holding grudges has a rotting effect on your soul.
Let go and let be. You do not have to be best friends with the person that wronged you but you should love them: meaning you should wish them to be happy.

Forgiving yourself is harder.
You are your own worst critic. Even when others and God have forgiven you, can you forgive yourself for what you have done no matter how minor or major the transgression?
I want to define two terms before moving on with my sermon of sorts.
Guilt and Regret are two different things.
Guilt is recognizing what you've done wrong and believing you are unworthy of love because of it.
Regret is recognizing what you have done wrong and resolving not to do it again.
Now class, which of the above is a healthy response?
Yes, regret.
By forgiving yourself and showing regret, you are not saying that what you've done is now ok but you are allowing yourself to move on.

If you are guilt ridden this is like your soul slowly rotting and going bad.
Guilt leads to more sin and bad habits.
Guilt can lead to drugs and alcohol, to bad relationships, to depression and harming yourself and those around you.
Example: if you have cheated on your spouse and do not forgive yourself and are in turn filled with guilt, you may never have a healthy relationship again.

My recommendation:
Recognize what you have done wrong
Ask for forgiveness of others if applicable
Ask for forgiveness of God
Forgive yourself
Show regret in that you will do your best to not do this again
Move on and be happy