For you should know that it is not easy both to keep your will in a condition conformable to nature and (to secure) external things: but if a man is careful about the one, it is an absolute necessity that he will neglect the other.
 Epictetus, Enchiridion (125). copy citation

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Author Epictetus
Source Enchiridion
Topic necessity neglect
Date 125
Language English
Reference
Note Translated by George Long
Weblink https://en.wikisource.org/wiki/Encheiridion_of_Epictetus_(George_Long)

Context

“If you would improve, submit to be considered without sense and foolish with respect to externals. Wish to be considered to know nothing: and if you shall seem to some to be a person of importance, distrust yourself. For you should know that it is not easy both to keep your will in a condition conformable to nature and (to secure) external things: but if a man is careful about the one, it is an absolute necessity that he will neglect the other. ==XIV==
If you would have your children and your wife and your friends to live forever, you are silly; for you would have the things which are not in your power to be in your power, and the things which belong to others to be yours.” source