If you had to say it to an eight-year-old, in a short time.
I would say that--you are really responsible for the world in which you live. If others happen to come along and join you in the spirit of your endeavor and your objectives to make the world a better place then you're the richer for it. But even if they don't exist, you still have your inner self to answer to. You still have, you, to deal with. And I think that those who put themselves in the service of life and the betterment of their fellow human beings are the ones who are on the best mission, the ones who are going to receive the greatest rewards from that experience.