Extreme heroism springs from something that no scientific theory can fully explain; it's an illogical impulse that flies in the face of biology, psychology, actuarial statistics, and basic common sense.
Nature does not capriciously scatter her secrets as golden gifts to lazy pets and luxurious darlings, but imposes tasks when she presents opportunities, and uplifts him whom she would inform. The apple that she drops at the feet of Newton is but a coy invitation to follow her to the stars.