"God has got me completely surrounded." That is the observation that David goes to great lengths to make here. God is in the highest heaven and the lowest place on earth. He is in life and in death. He is on the land and the sea. He knows every person intimately because He built us all in our mother's wombs. There is no escaping the intimacy of God's knowledge and presence.
God is before me and behind me at all times. He is there in the gains and in the losses. He is there in the blessings and the difficulties. His hand is always on me. Real faith knows this and accepts the encouragement to never run from that truth.
The worst delusion I could believe then is that God does not exist. The second is that He does not care for me. No matter how else I may struggle... may misunderstand or may be misunderstood, I can always, always, ALWAYS trust in God's faithful, unfailing presence and care for me.