But we may, for the good of others, engage in heroic acts of love: “And when the person sacrifices to the common good of the city that which is dearest to it, suffers torture and gives its life for the city, in these very acts because it wills what is good and acts in accordance with justice, it still loves its own soul, in accordance with the order of charity, more than the city and the common good of the city,” just as the hermit, who, “seeming to forget the city,” contemplates beauty and truth, and in so doing, “still serves the common good of the city and in an eminent fashion.”
How does my neighbor's sexual behavior affect my life, today, right now? I don't suppose "breaking my heart" counts. The truth is, I don't think we can claim to know how any one, isolated human act affects the lives of human beings--now, in the past, or in the future. We're too small.
But we can know THAT every action affects every human being who ever existed or will exist. I know that what Margaret Sanger--even though she never imagined that I, Erika, would exist--believed 100 years ago changed forever the world in which I live every day. I know what St. Peter did on Good Friday before dawn changed forever how I can hope in mercy--even though he lived worlds and ages away. I know that what the Russian Tsar did to a little village in Lithuania in 1904 frightened my grandparents into leaving, and that means that I exist (thank you, Russian Tsar?). I know that because my parents cared about what I chose to do with my body, I became a woman who could marry Todd and have three beautiful girls. We cannot know that immense good, or evil, our choices bring to other human beings.
But we know with certainty: No man in an island.