“Learn to control ego. Humans hold their dogmas and biases too tightly, and we only think that our opponents are dogmatic! But we all need criticism. Criticism is the only known antidote to error.”

"On Freedom" in All Life is Problem Solving (1999)
Context: When I speak of reason or rationalism, all I mean is the conviction that we can learn through criticism of our mistakes and errors, especially through criticism by others, and eventually also through self-criticism. A rationalist is simply someone for whom it is more important to learn than to be proved right; someone who is willing to learn from others — not by simply taking over another's opinions, but by gladly allowing others to criticize his ideas and by gladly criticizing the ideas of others. The emphasis here is on the idea of criticism or, to be more precise, critical discussion. The genuine rationalist does not think that he or anyone else is in possession of the truth; nor does he think that mere criticism as such helps us achieve new ideas. But he does think that, in the sphere of ideas, only critical discussion can help us sort the wheat from the chaff. He is well aware that acceptance or rejection of an idea is never a purely rational matter; but he thinks that only critical discussion can give us the maturity to see an idea from more and more sides and to make a correct judgement of it.

Lerne Widerspruch ertragen. Sei nicht kindisch eingenommen von deinen Meinungen.
Über den Umgang mit Menschen (1788)

The 4-Hour Workweek (2007)

Source: Conjectures and Refutations: The Growth of Scientific Knowledge (1963), Ch. 1 "Science : Conjectures and Refutations"
Context: The history of science, like the history of all human ideas, is a history of irresponsible dreams, of obstinacy, and of error. But science is one of the very few human activities — perhaps the only one — in which errors are systematically criticized and fairly often, in time, corrected. This is why we can say that, in science, we often learn from our mistakes, and why we can speak clearly and sensibly about making progress there.

Source: Translations from the Poetry of Rainer Maria Rilke

With Norton Mezvinsky.
Jewish Fundamentalism In Israel (1997)

Preface (Scribner edition, 1872) <!-- New York, Scribner p xx -->
Chips from a German Workshop (1866)
Context: He must be a man of little faith, who would fear to subject his own religion to the same critical tests to which the historian subjects all other religions. We need not surely crave a tender or merciful treatment for that faith which we hold to be the only true one. We should rather challenge it for the severest tests and trials, as the sailor would for the good ship to which he trusts his own life, and the lives of those who are dear to him. In the Science of Religion, we can decline no comparisons, nor claim any immunities for Christianity, as little as the missionary can, when wrestling with the subtle Brahmin, or the fanatical Mussulman, or the plain speaking Zulu.

Wen Jiabao (2008) cited in: Transcript of interview with Chinese Premier Wen Jiabao, 28 September 2008, CNN http://edition.cnn.com/2008/WORLD/asiapcf/09/29/chinese.premier.transcript/index.html,

Book XXX, sec. 30
History of Rome