There was a man in the history of David called Doeg, the Edomite. He seemed to be a spokesman of King Saul who was responsible for the killing of God's priests. It is said of him that he loved evil more than good, and lying rather than truth. He is accused of having a deceitful tongue. David the author states that he will be destroyed by God. When this is known by a virtually good man it should result in fear of God and a turning away from evil. This is what happens when we make God our trust. This is what happens when we trust in something besides God.
David in those days spent a lot of time being chased by Saul and the likes of this man. Even though this psalm begins with a fear of men like Doeg it ends up with praise for God and His ways. David describes himself as a green olive tree. That speaks of a rich life. We do want that kind of life even in the midst of difficulty.