To get back to the original question:
My father told me as a child of infantry soldiers being issued with grenades in times of war. These grenades become soiled, and require cleaning from time to time. To clean a grenade properly the pin must be removed, but it will not go off if the handle is properly held. However, if the hand slips during the cleaning process, and the grenade is about to go off, it is polite to fold oneself about the grenade and die without inconveniencing anyone else. My father used this example from his experience to teach me of the virtue in self-sacrifice. Whereas this was the WWII practice, and the modern way of doing the job involves a strong rubber band as a safety device, I understand that the principles are still taught in the same way, so that soldiers react to grenades in order to protect others.