The underlying assumption here is incorrect, that is, that greatness involves saving the world in some epic way. I, however, see greatness in one who sacrifices himself for another, no matter how small the task. From the stay-at-home mom who spends most of her time caring for a small child to Captain Kirk's father who sacrificed himself for the whole ship (newest ST movie), there is greatness to be found in all of them, and one is not necessarily greater than the other, for they both involve elevating the other's interests above your own.