For man is more diseased, more uncertain, more changeable, more unstable than any other animal, there is no doubt of it—he is the diseased animal
 Friedrich Nietzsche, On the Genealogy of Morality (1887). copy citation

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Author Friedrich Nietzsche
Source On the Genealogy of Morality
Topic doubt animal
Date 1887
Language English
Reference
Note Translated by Horace B. Samuel
Weblink https://en.wikisource.org/wiki/The_Genealogy_of_Morals

Context

“You understand me already: this ascetic priest, this apparent enemy of life, this denier—he actually belongs to the really great conservative and affirmative forces of life. . . . What does it come from, this diseased state? For man is more diseased, more uncertain, more changeable, more unstable than any other animal, there is no doubt of it—he is the diseased animal: what does it spring from? Certainly he has also dared, innovated, braved more, challenged fate more than all the other animals put together; he, the great experimenter with himself, the unsatisfied, the insatiate, who struggles for the supreme mastery with beast, Nature, and gods, he, the as yet ever uncompelled, the ever future, who finds no more any rest from his own aggressive strength, goaded inexorably on by the spur of the future dug into the flesh of the present:—how should not so brave and rich an animal also be the most endangered, the animal with the longest and deepest sickness among all sick animals?” source