Barry Eisler said this quote

Most people are like sheep. Nice, harmless creatures who want nothing more than to be left alone so they can graze. But then of course there are wolves. Who want nothing more than to eat the sheep.But there’s a third kind of person. The sheepdog. Sheepdogs have fangs like wolves. But their instinct isn’t predation. It’s protection. All they want, what they live for, is to protect the flock.