David was upset with those who wronged others . . . Rightly so! However, he left it up to God to deal with them. Though early in this psalm, he asks for harm to come to them, he realizes that vengeance is the Lord's! (Romans 12:19)
Things do not always go right for us. It seems as though the more We do to honor God and do right, the more we lose and those doing evil win! That might be true. However, God knows. He cares. He sees. He will have His justice one day!
That same David also wrote: Wait, I say, on the Lord. (Psalm 27:14) Listen to Jesus from the Sermon on the Mount . . . .