It is often painful to forget the past because its pain is mixed with reward. An effort to absolutely forget is harmful, remember with honesty and with gratitude. It may even be unhealthy to forget the past. But conversely it may be unhealthy to remember the past. For many, the past has greater potential to create problems than it has to provide blessings.
Most people forget the past selectively .
Generally we seek to avoid evidences of our helplessness, our mortality, our lack of control. We may even seek to hide the past. The past often gives us problems. Living in the past is unhealthy. Ignoring the past may stunt future growth.