“Then you know what to avoid. Do the exact opposite of what he did. His administration at the Foreign Office was one long crime.”
John Bright to Lord Rosebery in 1886, after asking him whether he had read about Palmerston's policies at the Foreign Office. (The Fifth Earl of Rosbery's journal, 17 March 1886)
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Henry Temple, 3rd Viscount Palmerston 72
British politician 1784–1865Related quotes

“What did I know, what did I know
of love's austere and lonely offices?”
Those Winter Sundays (lines 13-14)

“Do you know what a foreign accent is? It's a sign of bravery.”
Source: Battle Hymn of the Tiger Mother

“What is wanted is not the will to believe, but the will to find out, which is the exact opposite.”

About the 2018 Russia–United States summit, That was treason, Donald Trump. We all saw it https://www.theglobeandmail.com/opinion/article-that-was-treason-donald-trump-we-all-saw-it/ (July 16, 2018), The Globe and Mail.

At a rally in Grand Rapids, Michigan http://edition.cnn.com/videos/politics/2016/10/31/donald-trump-james-comey-has-guts-grand-rapids-sot.cnn shortly after Comey announced the FBI would investigate further emails relating to Hillary Clinton, but before his statement that no incriminating information was found within them (31 October 2016)
2010s, 2016, October

Salon.com column http://www.salon.com/mwt/col/waldman/2005/04/25/limon/index1.html

What do you mean by you?"
volume I; lecture 8, "Motion"; section 8-1, "Description of motion"; p. 8-2
The Feynman Lectures on Physics (1964)

“What we need is not the will to believe, but the wish to find out, which is its exact opposite.”
This was not Wordsworth's viewpoint at all. The words are in fact those of Bertrand Russell in his Sceptical Essays (1928), p. 157.
Misattributed