The first chabad Rebbe, Rabbi Shneur Zalman of Liadi, once had a conversation with an individual that was known to be a great Torah scholar with exemplary character traits.
In the conversation the Rebbe said the following:
“Even animals have good character traits, but they are natural. The raven in naturally cruel while the eagle is naturally merciful.
The character traits that are demanded of a human being are that he act in a way not determined by nature but by intellect. For this to be accomplished, work is entailed.”
When this individual realized that his entire life, he had merely been acting like an animal, he promptly fainted.
(Sefer HaMaamorim, 5710, Pg. 88)
