Editor's Note: The following illustration was adapted from an article by Michael Wheeler, a professor at Harvard Business School.

According to Major David Dixon, recently retired from the U.S. Marine Corps, from Day 1 every Marine is taught to live a life worthy of a Marine. They're also taught to hold one another accountable to that standard of excellence. Dixon says,

If the Marine next to you is falling asleep in class, you must have the moral courage to wake him up and motivate him to stay awake. If you are caught sleeping in class at boot camp, not only do you get in trouble for laziness, but the Marine to your left and to your right get in trouble for lack of moral courage because they should have corrected you when you were in the wrong.

There's a graphic example of this principle from a unit of British Marine commandos. During the war in Afghanistan, a unit came across an insurgent, badly wounded but unarmed. One of the British Marine soldiers, seething with rage, pointed his pistol at the man. He told the man to die and then pulled the trigger. The Marine's parting words were "It's nothing you wouldn't do to us." The solider then turned to his fellow commandos and said, "Obviously this doesn't go anywhere, fellas. I just broke the Geneva Convention." But word did get out in the following days, and that commando was found guilty of murder.

Could anything been said or done to prevent the tragedy? Some military experts believe that the murder could have been prevented if just one other Marine in that unit had the courage to confront their fellow-soldier and hold him accountable. It would have taken only four simple words: "Marines don't do that."