A surgical principle that one learns in medical school. In EMT school, in nursing school, in hospitals and no doubt, in war zones.
As medical students we hit the wards in our third year. The general surgery training was five years when I was in medical school. Usually the fifth year resident or the attending surgeon would use this during a surgery when a first year intern was ignoring a bleeder in the operating room, or dithering over what to do first with a trauma patient.
Trauma, it's still: ABC. Airway, breathing, circulation. If there is no airway, the bleeding doesn't much matter, does it? Then the patient has to be breathing. Then the heart has to be beating. Then deal with the arm that has been cut off..... actually if there is an artery pumping from the arm, you've already checked off circulation! Go team!