Five hundred years before Christ was born, the Greek philosopher Heraclitus told his students that "everything changes except the law of change". He said: "You cannot step in the same river twice." The river changes every second; and so does the man who stepped in it. Life is a ceaseless change. The only certainty is today. Why mar the beauty of living today by trying to solve the problems of a future that is shrouded in ceaseless change and uncertainty-a future that no one can possibly foretell?
Dale CarnegieLet's find and remedy all our weaknesses before our enemies get a chance to say a word. That is what Charles Darwin did. ...When Darwin completed the manuscript of his immortal book "The Origin Of Species" he realized that the publication of his revolutionary concept of creation would rock the intellectual and religious worlds. So he became his own critic and spent another 15 years checking his data, challenging his reasoning, and criticizing his conclusions.
Dale CarnegieCriticism is futile because it puts a person on the defensive and usually makes them strive to justify themselves. Criticism is dangerous, because it wounds a person's precious pride, hurts their sense of importance, and arouses resentment.
Dale Carnegie