If you haven't seen the movie, I highly recommend it.
Wayne Kyle speaking to his sons as they ate dinner:
"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 sheepdog."
From "American Sniper" (2014)
Based upon the story of Chris Kyle (1974-2013), US Navy, Chief Petty Office, Sniper Element, Platoon "Charlie", SEAL Team 3
Eyes Front Gentlemen. Live. Learn. Lead.