Hatred

I'm glad that at least someone in this Earth, knows hatred do not solve any problems at all.
The burning hatred in fact has a reverse psychological effect on your personal life. It doesn't affect the person you hate, it just affects your own life.
The person that you simply hate, might just be well off moving on with life, not even thinking about you. And yet, there you are still living in the moment of trying to hate the person.

To not repeat mistakes is to forgive and let live.
Instead, learning from other's mistakes and not committing the same exact mistake you hate.
The cliche thing is that, whilst hating this person so much, you change and behave exactly like the person you hate. Irony.

Always be kind, to yourself, and to others. Don't suppress yourself with feelings of hatred, nor anger. It'll just repeat themselves again, right in your own future.