Letters from a Stoic
Seneca · 65
"The fear of death — more precisely, the fear of wasted time, since death only reveals how much time was already squandered — is the central problem philosophy exists to solve, and solving it requires treating time, not money, as your only truly non-renewable asset."
Written as a real correspondence to his friend Lucilius late in Seneca's life, these letters are practical Stoicism applied to an actual life — his own, as a wealthy statesman under an unstable emperor — rather than abstract theory. His most quoted line, that we are not given a short life but we make it short, reframes the anxiety of mortality: the problem was never that life is brief, it's that most of it gets lost to distraction, busyness performed for others, and postponed living.
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Meditations
"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."