“It is a capital mistake to theorise before one has data.”
Source: The Adventures of Sherlock Holmes
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Arthur Conan Doyle 166
Scottish physician and author 1859–1930Related quotes

“In reality, the labourer belongs to capital before he has sold himself to capital.”
Vol. I, Ch. 23, pg. 633.
(Buch I) (1867)

“We all make mistakes but one has to move on.”

“Mistakes are always forgivable, if one has the courage to admit them.”

In 1980, during his inspection tour in Tibet, as quoted in Southern Mongolia: Self-Determination Activist Tortured in Prison and Kept Under House Arrest https://unpo.org/article/19652?id=19652

Letter to Russian Premier Gorbachev, January 1989. http://politicalquotes.org/node/68478
Foreign policy

“There is no mistake; there has been no mistake; and there shall be no mistake.”
In response to William Huskisson declaring there had been a mistake, and he had not intended to resign, after Wellington chose to interpret a letter to him detailing his obligation to vote for a measure opposed by him as a letter of resignation. As quoted in The Military and Political Life of Arthur Wellesley: Duke of Wellington (1852) by "A Citizen of the World", and in Wellingtoniana (1852), edited by John Timbs.

Despite all the veneration that I feel for this man, whom by the way I respect more as a master saddle-maker than as a Reich president, I simply have to be astonished. Gentlemen, where is the "beauty and dignity"?
01/23/1925, speech in the Bavarian regional parliament ("Kampf dem Weltfeind", Stürmer publishing house, Nuremberg, 1938)
Original: Wenn man Euch reden hört, dann habt Ihr immer den Kapitalismus bekämpft. In Wirklichkeit habt Ihr den Kapitalismus erst in den Sattel gehoben. In dieser Republik hat sich der Kapitalismus ausgewachsen wie niemals zuvor. Mag man über den alten Staat denken wir man will, eines steht fest: so verlumpt war er nicht wie der, den Ihr uns gebracht habt! …
Was soll man dazu sagen, wenn ein Reichspräsident Ebert den jüdischen Schurken Barmat in Briefen mit "Mein lieber Barmat" anredet und ihn am Schlusse mit "Dein Ebert" grüßt? Bei aller Ehrfurcht, die ich vor dem Mann habe, den ich übrigens als Sattlermeister weit mehr schätze denn als Reichspräsident, muss ich mich doch sehr wundern. Meine Herren, wo ist da "Schönheit und Würde"?

Said to Enver Hoxha, on his visit to China in 1956, as quoted in Hoxha's (1986) The Artful Albanian, (Chatto & Windus, London), ISBN 0701129700