I agree that it meant to be a figure of speech in many regards however alasdairm mentioned that some people probably have a small group of people, often family and friends, for whom the phrase would take on literal meaning. For example my brother, sister, and mother and even two of my ex's are people for whom I would definitely sacrifice my life. I mean I don't really even like living that much so I'd probably be willing to take a bullet for even more people if I honestly thought they wanted to live more, they would do more good for the world than me, they were more important to their families than I am to mine, etc... like I'd die before my cousin easily because her father, my uncle, already had his wife, my aunt, and my other cousin, his daughter, die and it would be horrible for him to lose another child when I'm one of three children and my parents both still have each other. So it depends on the person and how much they really cling to life and how they react in crisis situations. I know I do well under extreme duress such as medical emergencies, life or death situations, being interrogated/chased by the police; however minor anxieties flip me out such as social anxieties, stressful sports situations, getting yelled at by parents, etc....