A passage from Seneca
Seneca, On Tranquility of Mind XIII
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It is not the poor man who lacks much, but the rich man who desires more, that is poor.
Related passages
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Your present opinion founded on understanding, your present conduct directed to social good, your present disposition contented with everything that happens — that is enough.
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Everything you're trying to reach — by taking the long way round — you could have right now, this moment. If you'd only stop thwarting your own attempts.
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Every nature is contented with itself when it goes on its way well; and a rational nature goes on its way well, when in its thoughts it assents to nothing false or uncertain.