If a man will begin with certainties, he shall end in doubts; but if he will be content to begin with doubts he shall end in certainties - Francis Bacon, 1605
You must be the change you wish to see - M. Ghandi
Far better an approximate answer to the right question, which is often vague, than an exact answer to the wrong question, which can always be made precise - John W. Tukey, 1962