A stupid man does not observe that persons, who apparently act independently of each other, are really in collusion; he is therefore easily mystified, and outwitted; he does not discern the hidden motives of proffered advice or expressions of opinion, &c.
 Arthur Schopenhauer, The World as Will and Representation (1819). copy citation

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Author Arthur Schopenhauer
Source The World as Will and Representation
Topic advice expression
Date 1819
Language English
Reference
Note Translated by R. B. Haldane and J. Kemp
Weblink http://www.gutenberg.org/files/38427/38427-h/38427-h.html

Context

“A stupid person has no insight into the connection of natural phenomena, either when they follow their own course, or when they are intentionally combined, i.e. , are applied to machinery. Such a man readily believes in magic and miracles. A stupid man does not observe that persons, who apparently act independently of each other, are really in collusion; he is therefore easily mystified, and outwitted; he does not discern the hidden motives of proffered advice or expressions of opinion, &c. But it is always just one thing that he lacks—keenness, rapidity, ease in applying the law of causality, i.e. , power of understanding. The greatest, and, in this reference, the most instructive example of stupidity I ever met with, was the case of a totally imbecile boy of about eleven years of age, in an asylum.” source