For the kind of sorrow God wants us to experience leads us away from sin and results in salvation. There’s no regret for that kind of sorrow. But worldly sorrow, which lacks repentance, results in spiritual death.
For the sorrow that is according to the will of God produces a repentance without regret, leading to salvation, but the sorrow of the world produces death.
For what human being knows what is truly human except the human spirit that is within? So also no one comprehends what is truly God's except the Spirit of God.