Psalm 23 is among the most popular ones in all of Tehillim. It is no accident that it follows Psalm 22, one of the most depressing ones. One can go from misery to happiness in the blink of an eye if one relies on God.
A Psalm of David. The Lord is my Shepherd, I shall not want. He lays me down in green pastures. He leads me beside tranquil waters. My soul He restores. He leads me on the path of tzedek [usually translated as either righteousness or justice] for the sake of His Name. Even though I walk through the valley of the shadow of death, I will fear no evil, for you are with me; your rod and your staff, they comfort me. You prepare a table before me in the presence of my enemies: you anoint my head with oil; my cup runneth over. Surely goodness and lovingkindness shall follow me all the days of my life; And I shall dwell in the house of the Lord forever. (Psalm 23: 1-6).