'And so also of what properly belongs to man; shall it be said that the mind of any man was without benevolence and righteousness? The way in which a man loses his proper goodness of mind is like the way in which the trees are denuded by axes and bills. Hewn down day after day, can it the mind retain its beauty? But there is a development of its life day and night, and in the calm air of the morning, just between night and day, the mind feels in a degree those desires and aversions which are proper to humanity, but the feeling is not strong, and it is fettered and destroyed by what takes place during the day. This fettering taking place again and again, the restorative influence of the night is not sufficient to preserve the proper goodness of the mind; and when this proves insufficient for that purpose, the nature becomes not much different from that of the irrational animals, and when people now see it, they think that it never had those powers which I assert. But does this condition represent the feelings proper to humanity?
'Therefore, if it receive its proper nourishment, there is nothing which will not grow. If it lose its proper nourishment, there is nothing which will not decay away.
'Confucius said, "Hold it fast, and it remains with you. Let it go, and you lose it. Its outgoing and incoming cannot be defined as to time or place." It is the mind of which this is said!'~ James Legge translation via nothingistic.org ~
Go here to read the introductory post to this serialized version of the Works of Mencius.