For Marcus Aurelius, the quality of our day is up to each one of us. We have little power to choose what happens, but we have complete power over how we respond. It all starts with setting the expectations that make it clear that no matter how much hardship we encounter—how much pain and loss, dishonesty, ingratitude, unfairness, and jealousy—we can still choose peace and imperturbability. And from that place of imperturbability—or ataraxia, as the Greeks called it—we can much more effectively bring about change.