"The world is a tragedy to those who feel, but a comedy to those who think."

Actions are right in proportion as they tend to promote happiness； wrong as they tend to produce the reverse of happiness.

The moment you stop trying is the moment you stop learning.

The end of history will be a very sad time. The struggle for recognition, the willingness to risk one's life for a purely abstract goal, the worldwide ideological struggle that called forth daring, courage, imagination, and idealism, will be replaced by economic calculation, the endless solving of technical problems, environmental concerns, and the satisfaction of sophisticated consumer demands.