The Greek meaning of the word "forgetting" that Paul used in Philippians 3:13 means "to neglect."  Webster defines "neglect" as "to give little attention or respect to."  When God instructed us to "forget" our past, He didn't expect us to wipe out the memories of the loved ones we lost or painful experiences that we learned life lessons from.  Instead, I believe God is saying that while we might remember those things, He does not want us to give so much attention to it that we can't move forward.

Likewise, there are people that have had very positive and happy things happen in their past, and they continue to compare every new situation and person to that past joy or past event.  They are then unable to experience the awesome and wonderful things that God has for them.

I imagine a new year to be like standing in an airport waiting in baggage claim after a long journey.  As the bags go by, some individuals continue to load bag after bag on carts surely to be weighed down while others walk right past baggage claim carrying just what they need to quickly be on their way!