Our past is our foundation until we release negative beliefs about it. Often these are relationships in which we believe we could have done better. Sometimes it is a feeling of having been hurt, or we feel guilt of having hurt others. We often have negative pictures of ourselves stemming from the past. Right now, you could look back to a time in your past when something happened, and then you could not understand its reasons.
Now looking back at it, you see why it had to happen and how it shaped your life. Look at relationships or jobs you had and notice how they have helped you evolve. The more you dislike something the more it seems to stick while loving something, even our past, will free us. The past can be released by accepting it. Now, that indeed is the issue, we often think we have, but all we have done is pushed it aside so that we do not have to think about it any longer. That is not acceptance but suppression.
In therapy, specifically hypnotherapy, we can change emotions and beliefs that are troublesome and feelings that may have been there for what seems forever, can often just dissolve in one session.