As much as we all carry around yesterday, we can never ever take it back. Never ever change one thing about it other than how we choose to react and move on from it. Sometimes we waste years and years of our tomorrows dwelling on all the negative that yesterday's permanence holds.
This isn't only true for things we've done to others but the things that others have done to us. No matter how much we wish we could go back and change decisions or choices, there are others who wish they could as well. It's utterly important to remember that everything we did or can do has already been forgiven and paid for on the cross. Christ knew we would do all those things and others would do those things to us and He provided a loving sacrifice to cover those hurts so we wouldn't have to suffer them ourselves. If we choose to dwell on them, we are choosing to disregard His offering of hope for a better life and choose the bitter life, instead.
Are we going to remember? Of course...but we mustn't get caught there.