Phillip Keller is a pastor and author, who for eight years was himself a shepherd. Out of that experience he has written a helpful book entitled A Shepherd Looks at Psalm 23. Sheep do not lie down easily, Keller says. In fact, "It is almost impossible for them to be made to lie down unless four requirements are met. Owing to their timidity they refuse to lie down unless they are free of all fear. Because of the social behavior within a flock, sheep will not lie down unless they are free from friction with others of their kind. If tormented by flies or parasites, sheep will not lie down