Ch'âu pursued, 'I venture to ask what you mean by your vast, flowing passion-nature!' The reply was, 'It is difficult to describe it.Go here to read the introductory post to this serialized version of the Works of Mencius.
'This is the passion-nature: It is exceedingly great, and exceedingly strong. Being nourished by rectitude, and sustaining no injury, it fills up all between heaven and earth.
'This is the passion-nature: It is the mate and assistant of righteousness and reason. Without it, man is in a state of starvation.
'It is produced by the accumulation of righteous deeds; it is not to be obtained by incidental acts of righteousness. If the mind does not feel complacency in the conduct, the nature becomes starved. I therefore said, "Kâo has never understood righteousness, because he makes it something external."
'There must be the constant practice of this righteousness, but without the object of thereby nourishing the passion-nature. Let not the mind forget its work, but let there be no assisting the growth of that nature. Let us not be like the man of Sung.
'There was a man of Sung, who was grieved that his growing corn was not longer, and so he pulled it up. Having done this, he returned home, looking very stupid, and said to his people, "I am tired to-day. I have been helping the corn to grow long." His son ran to look at it, and found the corn all withered. There are few in the world, who do not deal with their passion-nature, as if they were assisting the corn to grow long. Some indeed consider it of no benefit to them, and let it alone: they do not weed their corn. They who assist it to grow long, pull out their corn. What they do is not only of no benefit to the nature, but it also injures it.'
~ James Legge translation via nothingistic.org ~