Ultimately holding onto anger is not only as one psychologist explained it in a lecture, like taking poison and waiting for your enemy to die, but is also the reason why there is evil in the world. Because as the Kabbalah teaches, we all want to be happy and no one wants to live in pain, but if we G-d-forbid hold onto resentments, then not only are we stewing, but as people – as the Talmud writes, are jealous of the good that others have – hence, the greatest jealousy that exists, is not over another person’s car, beautiful home etc. rather over happiness. So here’s the equation of evil – I miserable – you happy – hence I seek to destroy your happiness (this of course explains the bizarre phenomena of bullying, antisemitism, terrorism etc.)