A passage from Epictetus
Epictetus, Discourses IV.6
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When you have made the right the only good, and the wrong the only evil, what room is there for fear or anxiety? Nothing can harm you but your own wrongdoing.
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.