A passage from Epictetus
Epictetus, Discourses IV.7
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Do not be proud of any excellence that is not your own. If the horse were proud and said, 'I am handsome,' it would be supportable. But when you are proud of your horse, your house, or your clothes, you are proud of what belongs to another.
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.