There are three types of people in this world: sheep, wolves, and sheepdogs.
Some people prefer to believe that evil doesn't exist in the world,
and if it ever darkened their doorstep, they wouldn't know how to protect themselves.
Those are the sheep.
Then you've got predators, who use violence to prey on the weak.
They're the wolves.
And then there are those blessed with the gift of aggression,
an overpowering need to protect the flock.
These men are the rare breed who live to confront the wolf.
They are the sheepdogs.
— Wayne Kyle in American Sniper (2014)
Two quick observations here.
(1) There are three kinds of people in the world: those who think there are three kinds of people, those who don't, and those who tweak and re-cycle one old joke about "two kinds of people in the world."