Stoics
One idea, built into a complete philosophy of life and carried for five centuries by a merchant, a water-carrier, a logician, a statesman, a freed slave, and an emperor. The Stoics held that the only true good is virtue, a well-governed mind, and that everything else (health, wealth, reputation, even life itself) is an "indifferent," neither good nor bad in itself. From that one claim follows the rest: that a good life is available to anyone, in any circumstance, because it depends not on what happens but on the judgments a person makes about what happens. This is the story of how that idea was founded, systematized, lived at the top and the bottom of Roman society, and then dispersed into Christianity, the English language, and a modern therapy.
