From an anecdote in the New York Times:
The German naturalist Alexander von Humboldt told a friend, a Parisian doctor, that he wanted to meet a certifiable lunatic, he was invited to the doctor’s home for supper.
A few days later, Humboldt found himself placed at the dinner table between two men. One was polite, somewhat reserved, and didn’t go in for small talk. The other, dressed in ill-matched clothes, chattered away on every subject under the sun, gesticulating wildly, while making horrible faces.
When the meal was over, Humboldt turned to his host. “I like your lunatic,” he whispered, indicating the talkative man. The host frowned. “But it’s the other one who’s the lunatic. The man you’re pointing to is Monsieur Honoré de Balzac.”