Meditations
Marcus Aurelius · 180
"Peace of mind comes from rigorously separating what's in your control — your judgments, intentions, reactions — from what isn't — external events, other people, outcomes, even your own body — and directing all effort at the former while accepting the latter without resistance."
Written as a private journal by a Roman emperor during military campaigns, never intended for publication — part of why it reads as unusually honest self-coaching rather than a polished treatise. Its core move, inherited from earlier Stoics, is the dichotomy of control: events themselves are neutral, only your judgment about them causes suffering, so the discipline is to catch yourself assigning good or bad to something outside your control and correct it in real time.
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Utilitarianism
"The right action is whichever produces the greatest net happiness for the greatest number of people affected — an act is judged entirely by its consequences, not by the intentions behind it or any rule it follows."