It is the mature thing to move on. That's what Paul is saying in this scripture. If we are mature we should be able to forgive and forget. I was thinking about that and trying to come up with why it is so hard for some people to forgive, let alone forget. We probably all have trouble with this to some extent to be sure. Perhaps sometimes we think we are protecting ourselves from further hurt. But the second part of what Paul says he is doing is pressing on toward the goal to win the prize for which God called him heavenward in Christ Jesus. How can we press on if we won't get out of the past and forget what is behind?
This says to me that our focus is on ourselves when we can't forgive and move on. I have been there and it can become downright obsessive. I would brood and brood, think and think about what that person did. I would replay scenarios in my mind, acting out what should have happened, or acting out that person apologizing and changing. I couldn't go on with what God had for me to do while I was obsessing about my hurt feelings.
We can't afford to be unforgiving. Not only does it render us useless for the Kingdom, but God can't forgive us our sins while we harbor unforgiveness!
Matthew 6:14 - For if you forgive men when they sin against you, your heavenly Father will also forgive you.
Mark 11:25 - And when you stand praying, if you hold anything against anyone, forgive him, so that your Father in heaven may forgive you your sins.
We can't afford to live in the past so let's move on and allow Father God to heal us and restore us so that He can use us to our full potential for His Will!