A passage from Epictetus
Epictetus, Enchiridion 26
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The will of nature may be learned from things upon which we are all agreed. As, when our neighbour's boy has broken a cup... so, when your own cup is broken, you ought to be affected just as when another's cup was broken.
Related passages
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Begin the morning by saying to thyself, I shall meet with the busy-body, the ungrateful, arrogant, deceitful, envious, unsocial.
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Take away thy opinion, and then there is taken away the complaint, 'I have been harmed.' Take away the complaint, and the harm is taken away.
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If you are distressed by anything external, the pain is not due to the thing itself, but to your estimate of it; and this you have the power to revoke at any moment.