The past is gone and the future is yet to be. All we really have is this moment.
Life is like a river.
The river rarely, if ever, passes the same point twice. Some spend their whole lives trying to live in the past and others only brief moments. Our lives are right now, right this moment. We should look to the past only to learn from the mistakes we have made and the lessons we have learned. We may also look briefly to the past in consideration of fond memories and pleasant occurrences.