The Great Learning by Confucius

What is meant by "The regulation of one's family depends on the cultivation of his person" is this: -men are partial where they feel affection and love; partial where they despise and dislike; partial where they stand in awe and reverence; partial where they feel sorrow and compassion; partial where they are arrogant and rude. Thus it is that there are few men in the world who love and at the same time know the bad qualities of the object of their love, or who hate and yet know the excellences of the object of their hatred.

Hence it is said, in the common adage: A man does not know the wickedness of his son; he does not know the richness of his growing corn.