...is weight. Needless weight at that. And it poisons the one who holds on.
Part of the supernatural power of a Christian lies in the ability to forgive, empowered by the grace of God.
It's not always easy and our human feelings might not always agree, but with God's help it's always within our grasp (even if it is a long journey).
Does anyone come to mind when you think of unforgiveness? That person is probably the one you need to forgive. Whether you can speak to them or not, invite God into that place. Pray for help, and don't worry if your emotions are slow to align — it may take a while.