The Lord is my shepherd, I lack nothing. (Psalm 23:1 NIV)
King David was an experienced shepherd, he knew what it meant to take care of sheep. He was very protective of the sheep in his care and did not walk away when they were under attack by ferocious beasts (1 Samuel 17:33-37).
David was a warrior, his life was in constant danger. He lived on the edge. By declaring The Lord as his shepherd in this beautiful Psalm, he was highlighting His loving care, provision and protection. As far as he was concerned, he had everything he needed.