Marcus Aurelius, Meditations: Book 4:29
If one does not recognize the contents of the universe is a stranger in it, no less a stranger is the one who fails to recognize what happens in it. He is a fugitive if he runs away from the social principle; blind, if he shuts the eye of the mind; a beggar, if he depends on others and does not possess within him all the needs for life; a tumor on the universe, if he stands aside and separates himself from the principle of our common nature in disaffection with his lot (for it is nature which brings this about, just as is brought you about too); a social splinter, if he splits his own soul away from the soul of all rational beings, which is a unity.
Themes
Marcus Aurelius was a Roman Emperor from 161 to 180 AD. He was the last of the Five Good Emperors, and is also considered one of the most important Stoic philosophers.