The reasons people hang on to their past is quite varied and subjective. Different events, affect different people in different ways. The events we hang onto are always trying to teach us something. The first question to ask is:
What emotion(s) am I feeling about this?
Identifying the emotion will help you see how invested you are in this past event. There is a big difference to merely being frustrated to having full blown anxiety and anger. Frustration can be dealt with fairly easily but anxiety and depression over the past is a different issue all together. Either way, asking yourself these questions can help reveal what is really going on and help you release it.
What is normally happening when this memory or feeling comes up?
There is always a trigger. Think about what is usually happening around you when the painful memory comes up. Is it a person, place, thing or circumstance that triggers the past to come back and bother you? If so, it will be able to show you some blocks and barriers that you may have that need to be examined.
If I could go back in time to this person/event what would I say to them?
Sometimes we don't have closure to the past because we were not able to express ourselves properly in that moment. Go back to how you felt. Did you get to tell them how you really felt? Think about what you would have told them and note how you are feeling when you tell them. By expressing your feelings, even in your own mind, you are releasing negative emotional energy and can start to find some closure.
What need did I have that was not being met at that time?
Often, when we are hanging on to the past, it is because we had a need that wasn't being met. Maybe we needed to be heard and weren't. Perhaps your emotions or opinions were invalidated when they shouldn't have been. Perhaps you were struggling at the time and needed some understanding but were met with criticism instead. Find the need that wasn’t met and see how you can meet that need yourself.
How could I give this situation a new perspective?
Everything contains it's polar opposite. So this bothersome or painful event has a flip side. Can you stand in the other person's shoes for just a moment and see how they feel and what was going on with them? Were there other things going on with the event that you couldn't see then that you can see now? It's not condoning what happened. It's just if you can see the flip side you might be able to see why a person or circumstance played out the way it did. If this is about something you did, can you see where you were emotionally at the time and can you be easy on yourself and forgive yourself?
Examining another perspective can help us find compassion for others and ourselves so we can start to let go and heal.
What did this past event(s) teach me about myself and what I want?
The past and our even enemies are our greatest teachers. If the past is still creeping into our present day life, there must be something we need to learn from it still. The only reason we do or want anything in life is because we want to feel better. What would make you feel better about this past event? What could you have done differently? What is this person or circumstance showing you about you and what you truly want?
When we stop looking at things subjectively, just for a moment, and look at it objectively, as an observer, we can see humans just being humans and doing the very best they can each and every moment. If the past has come back to haunt you, you may want to look at what you are still doing, thinking or feeling that is making your past teacher, teach you in the present. If there is nothing left to learn. Then it is time to lay it down, move on and be free of it last.