The student of human nature can always discover some hobby, some accessible weakness and sensitive spot in their heart.
 Honoré de Balzac, Lost Illusions (1843). copy citation

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Author Honoré de Balzac
Source Lost Illusions
Topic weakness heart
Date 1843
Language English
Reference
Note Translated by Ellen Marriage
Weblink https://www.gutenberg.org/cache/epub/13159/pg13159.html

Context

“Men of this stamp are, in a certain sense, intellectual libertines. Everything is within their reach, consequently their fancy is jaded, and they will make immense efforts to shake off their indifference. The student of human nature can always discover some hobby, some accessible weakness and sensitive spot in their heart. Chaboisseau might have entrenched himself in antiquity as in an impregnable camp. "The man will be an antique to match, no doubt," said Etienne, smiling. Chaboisseau, a little old person with powdered hair, wore a greenish coat and snuff-brown waistcoat;” source