A passage from Epictetus
Epictetus, Enchiridion 3
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With regard to whatever objects either delight the mind or contribute to use or are tenderly beloved, remind yourself of what nature they are, beginning with the merest trifles: if you have a favorite cup, that it is only a cup; then if it is broken you can bear it.
Related passages
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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.
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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.