In Life on the Edge, Dr. James Dobson writes:

What are the characteristics of sheep that remind the Lord of you and me? What is he really saying when he refers to us in that way? Well, shepherds and ranchers tell us that these animals are virtually defenseless against predators, not very resourceful, inclined to follow one another into danger, and they are absolutely dependent on their human masters for safety. Thus, when David wrote, "We all, like sheep, have gone astray," he was referring to our tendency to move as an unthinking herd and away from the watchful care of the Shepherd.

I observed this herd instinct a few years ago in a documentary on television. It was filmed in a packing house where sheep were being slaughtered for the meat market. Huddled in pens outside were hundreds of nervous animals. They seemed to sense danger in their unfamiliar surroundings. Then a gate was opened that led up a ramp and though a door to the right. In order to get the sheep to walk up that ramp, the handlers used what is known as a "Judas goat." This is a goat that has been trained to lead the sheep into the slaughterhouse. The goat did his job very efficiently. He confidently walked to the bottom of the ramp and looked back. Then he took a few more steps and stopped again. The sheep looked at each other skittishly and then began moving toward the ramp. Eventually, they followed the confident goat to the top, where he went through a little gate to the left, but they were forced to turn to the right and went to their deaths. It was a dramatic illustration of unthinking, herd behavior and the deadly consequences it often brings.