A passage from Seneca
Seneca, Letters to Lucilius Letter 29
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Do not admit into thy company any man whom thou wouldst not admit into thy inner mind.
Related passages
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At dawn, when you have trouble getting out of bed, tell yourself: 'I have to go to work — as a human being.'
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Take care not to be Caesarified, or dyed with purple; for it does happen. Keep thyself then simple, good, pure, serious, free from affectation.
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It is a man's special privilege to love even those who wrong him.