Stoicism
A school of Hellenistic philosophy founded by Zeno of Citium in Athens around 300 BCE, teaching that virtue and reason are the only genuine goods, and that external events — fortune, misfortune, loss, reputation — need not disturb one's inner equilibrium. Stoics draw a sharp distinction between what is "up to us" (our judgments, desires, and responses) and what is not (health, wealth, and everything beyond our control); equanimity follows from accepting the latter and mastering the former. The tradition runs from Zeno through Epictetus, Marcus Aurelius, and Seneca, and has seen a sustained modern revival as a practical philosophy.