All things excellent are as difficult as they are rare.
"In computational learning theory, the challenge is not just to learn, but to understand how learning is possible."
解释：拥有绝色美貌的人，完全能够祸乱人的情志。
The first man who， having enclosed a piece of ground， bethought himself of saying 'This is mine，' and found people simple enough to believe him， was the real founder of civil society.
