I'm the worst at holding grudges. I'm stubborn and I don't like to say sorry, even when I know I'm wrong. However, I'm working on this. I made the conscious decision to move on from my past and whatever bad feelings that may lie there.
News flash: you can't change the past, no matter how badly you want to.
I know that someone just telling you to move on isn't going to magically heal you from whatever is holding you back. That's not how people work, and that's OK.
What's not OK is letting your past affect your future long after you should be over things.
There comes a time when it gets a little ridiculous to be holding onto your past so much that it defines every part of you. You aren't your past, you're you. You decide what people find out about you and how they interpret what you went through based on how you act.
Did you go through a bad breakup? Learn from it, pick yourself back up and start loving yourself instead. Did someone you love hurt your feelings?
Forgiveness is a virtue. You know you'd want to be forgiven, too.
I'm not saying you should never feel sad or broken. Being knocked down is a part of life. Bad things are inevitable, but they shouldn't control your life and put a damper on the good things that happen to you.
Once you've worked through the emotions and stresses that come with being hurt, ask yourself why it's important. If someone hurt you and doesn't know, tell them and move on. If a relationship is bringing more harm than good, walking away is the best thing to do. It's hard, but it's worth it.
Your driving force behind moving on should be gaining back your happiness, not getting revenge on whoever hurts you.
You get back the energies that you put out into the universe, make sure they're positive ones.