Source: Ideas have Consequences (1948), p. 49.
Quotes about difficulty
page 8

Duhamel, Cours d'Analyse de l'Ecole Polytechnique. Paris, Bachelier. vol i 1841 vol. ii. 1840.
The Differential and Integral Calculus (1836)

II. pp. 238-239
"On the Philosophy of the Asiatics" (1794)

No. 1.
Seventy Resolutions (1722-1723)

Augustus William Hare and Julius Charles Hare Guesses at Truth (London: Macmillan, ([1827-48] 1867) p. 7.
Misattributed

[Beecham admitted to Neville Cardus that he had made this up on the spur of the moment to satisfy an importunate journalist; he acknowledged that it was an oversimplification. (Neville Cardus: 'Sir Thomas Beecham, A Memoir', 1961)]

Source: Liberalism (1911), Chapter IV, "Laissez - Faire", p. 47.

Speech https://api.parliament.uk/historic-hansard/commons/1938/oct/05/policy-of-his-majestys-government#column_370 in the House of Commons (5 October 1938) against the Munich Agreement
The 1930s

Source: The Life of St. Teresa of Jesus (c.1565), Ch. I "Childhood and early Impressions" ¶ 4

"To the Indianapolis Clergy." The Iconoclast (Indianapolis, IN) (1883)

Address on the 18th anniversary of his coronation (2 November 1948) http://www.jah-rastafari.com/selassie-words/show-jah-word.asp?word_id=18ann

Quotes of Salvador Dali, 1971 - 1980, Dali interviewed by Victor Bockris, 1974

Daniel Buren, "Critical Limits," (1970), in: Buren, Five Texts, trans. Laurent Sauerwein (New York: John Weber Gallery, 1973), p. 45
1970s

Letter http://books.google.com/books?id=DVVffTwVVy4C&q=%22One+of+the+difficulties+with+all+our+institutions+is+the+fact+that+we've+emphasized+the+reward+instead+of+the+service%22&pg=PA166#v=onepage to Harold E. Moore (27 September 1949)

“Pursuit of Knowledge Under Difficulties”
Title of book (published 1830).

Guest of Honor speech at Aussiecon Two (August 1985), as published in Castle of Days (1992)
Nonfiction

RODIN, AUGUSTE. L'Art. Entretiens réunis par Paul Gsell, 1911

In re North, Ex parte Hasluck (1895), L. R. 2 Q. B. D. [1895], p. 269.
Spectrum: From Right to Left in the World of Ideas (2005), Ch. 6. "Plotting Values, Norberto Bobbio" (1998)
Inspire Yourself

Preface to Instructive ausgabe. Klavier-Etuden von Fr. Chopin, 1880.

existence
Science and the Unseen World (1929)

J.D. Bernal (1959/1969) Science in history Vol 3. p. 862; cited in: Ludwig von Bertalanffy (1968) General System Theory. p. 5-6

Quote from John Constable's letter to Rev. John Fisher (23 October 1821), as quoted in Richard Friedenthal, Letters of the great artists – from Blake to Pollock (Thames and Hudson, London, 1963), p. 41
1820s
What Will the Age of Aquarius Bring
One-Half of Robertson Davies (1977)

1920s, Second State of the Union Address (1924)

Letter to George Washington (May 1776)

The Uttarpara Address (1909)

Source: Think Big (1996), p. 239

1850s, The Present Aspect of the Slavery Question (1859)

Source: 1960s, A concept of corporate planning, 1969, p. 1 as cited in: Henry Mintzberg (1994) Rise and Fall of Strategic Planning. p. 98.

Memorandum to Clemenceau (28 April 1919), quoted in David Lloyd George, The Truth about the Peace Treaties. Volume I (London: Victor Gollancz, 1938), p. 428.
Source: A History of Economic Thought (1939), Chapter VI, Marx, p. 266

“While unbelief sees the difficulties, faith sees God between itself and them.”
(A.J. Broomhall. Hudson Taylor and China’s Open Century, Book Two: Over the Treaty Wall. London: Hodder and Stoughton and Overseas Missionary Fellowship, 1982, 62).

The Faith of Puppets: The Faith of Puppets (p. 18-9)
The Soul of the Marionette: A Short Enquiry into Human Freedom (2015)

Variant: An example may clarify more precisely the relation between the psychologist and the anthropologist. If both of them investigate, say, the phenomenon of anger, the psychologist will try to grasp what the angry man feels, what his motives and the impulses of his will are, but the anthropologist will also try to grasp what he is doing. In respect of this phenomenon self-observation, being by nature disposed to weaken the spontaneity and unruliness of anger, will be especially difficult for both of them. The psychologist will try to meet this difficulty by a specific division of consciousness, which enables him to remain outside with the observing part of his being and yet let his passion run its course as undisturbed as possible. Of course this passion can then not avoid becoming similar to that of the actor, that is, though it can still be heightened in comparison with an unobserved passion its course will be different: there will be a release which is willed and which takes the place of the elemental outbreak, there will be a vehemence which will be more emphasized, more deliberate, more dramatic. The anthropologist can have nothing to do with a division of consciousness, since he has to do with the unbroken wholeness of events, and especially with the unbroken natural connection between feelings and actions; and this connection is most powerfully influenced in self-observation, since the pure spontaneity of the action is bound to suffer essentially. It remains for the anthropologist only to resign any attempt to stay outside his observing self, and thus when he is overcome by anger not to disturb it in its course by becoming a spectator of it, but to let it rage to its conclusion without trying to gain a perspective. He will be able to register in the act of recollection what he felt and did then; for him memory takes the place of psychological self-experience. … In the moment of life he has nothing else in his mind but just to live what is to be lived, he is there with his whole being, undivided, and for that very reason there grows in his thought and recollection the knowledge of human wholeness.
Source: What is Man? (1938), pp. 148-149

To Leon Goldensohn, after being asked if Himmler trusted anyone (13 March 1946). Quoted in "The Nuremberg Interviews" - by Leon Goldensohn, Robert Gellately - History - 2004

1950s, Loving Your Enemies (Christmas 1957)

“One difficulty follows another very fast – but God reigns, not chance.”
(A.J. Broomhall. Hudson Taylor and China’s Open Century, Book Five: Refiner’s Fire. London: Hodder and Stoughton and Overseas Missionary Fellowship, 1985, 250).

Courage, www.blogspot.com http://spunkymonky.blogspot.com/2004/09/courage.html,

Source: Twenty Years at Hull-House (1910), Ch. 17

Letter to George Washington (January 1780)

Source: Seven Great Statesmen in the Warfare of Humanity with Unreason (1915), p. 60-61

Speech http://hansard.millbanksystems.com/commons/1931/mar/12/india in the House of Commons (12 March 1931).
1931
The Morality of Poetry
Primitivism and Decadence : A Study of American Experimental Poetry (1937)

August-Wilhelm Scheer, and Frank Habermann. " Enterprise resource planning: making ERP a success http://ecis.seattleu.edu/courses/ecis464spring04/Articles/Making%20ERP%20a%20Success.pdf." Communications of the ACM 43.4 (2000): 57-61.

Practical Sermons Designed for Vacant Congregations and Families (1841), Sermon VIII : God Is Worthy of Confidence, p. 123.

Munk debates – “21st Century will belong to China” – Kissinger, Zakaria, Ferguson, Li http://www.livestream.com/munkdebates/video?clipId=pla_937b4cf4-e0ea-4ed5-a458-6a3ba43769b8
2000s
Wondering how golden-crowned kinglets, which eat insects from open branches, survive the Maine winters, in "December 11 : Wind", p. 150
A Year in the Maine Woods (1995)

Preface
A Course of Lectures on Natural Philosophy and the Mechanical Arts (1807)

Call for Reckoning http://pewforum.org/deathpenalty/resources/transcript3.php3 - Pew Forum conference (25 January 2002). N.b. this speech was later modified into an article - God's Justice and Ours http://www.firstthings.com/article/2007/01/gods-justice-and-ours-32 which repeats much the same points.
2000s

§5.2
Notation as a Tool of Thought (1979)

Source: Social Problems (1883), Ch. 13 : Unemployed Labor

“If we can see our difficulties, there is a way of resolving them, or the hope of a way.”
The Glass Forest (1986)
" What Is Living and What Is Dead in Social Democracy? http://www.nybooks.com/articles/2009/12/17/what-is-living-and-what-is-dead-in-social-democrac/" (2009)

Zhang Zhijun (2014) cited in " China and Taiwan in first government talks http://www.bbc.co.uk/news/world-asia-china-26129171" on BBC, 11 February 2014.

Opening Keynote Address at NGO Forum on Women, Beijing China (1995)

Progress, Coexistence and Intellectual Freedom (1968), Dangers, Vietnam and the Middle East
Source: Gibbon's Decline & Fall (1996), Chapter 5 (p. 96)
The proposition that morale predicts productivity is just one specification of this.
Source: 1970s, Complex organizations, 1972, p. 115

The Education of Henry Adams (1907)

Autobiographical Essay (2001)

Enver Hoxha, Reflections on China, 1962-1972, vol. I http://redstarlibrary.org/?p=471 (Tirana: 8 Nëntori Publishing House, 1979)
Writings, Reflections on China, 1962-1972

Speech to the Trades Union Congress at Bridlington (7 September 1949), quoted 'Chronology, 18 August 1949 - 7 September 1949', Chronology of International Events and Documents, Vol. 5, No. 17 (18 August-7 September 1949), p. 583
1940s
"False Premise, Good Science", p. 138
The Flamingo's Smile (1985)
Dwarka (Gujarat). Burhãn-i-Ma‘sir, in Uttara Taimûra Kãlîna Bhãrata, Persian texts translated into Hindi by S.A.A. Rizvi, 2 Volumes, Aligarh, 1958-59. Vol. II, p. 218-19

“Man needs his difficulties because they are necessary to enjoy success.”
Source: Wings of Fire p. 90.

Speech during the general election of 1843, quoted in G. M. Trevelyan, The Life of John Bright (London: Constable, 1913), pp. 113-114.
1840s

Quote from Turner's letter to Mr. Hawkesworth, 24 December, 1849; as quoted in The life of J.M.W. Turner, Volume II, George Walter Thornbury; Hurst and Blackett Publishers, London, 1862, pp. 90-91
1821 - 1851
Individualism and Socialism (1933)
I. Bernard Cohen, Preface to Opticks by Sir Isaac Newton (1952)

Preface of M. Quetelet
A Treatise on Man and the Development of His Faculties (1842)

Michael J. Sandel, "Moral Argument and Liberal Toleration: Abortion and Homosexuality" (1989)

Excerpt from Atlantic Fleet Confidential Memorandum 2CM-41, sent on 24 March 1941. As quoted in History of United States Naval Operations in World War II, Volume One: The Battle of the Atlantic, September 1939-May 1943 (1948) by Samuel Eliot Morison, p. 52

Preface to the First American Printing (1950) Note: see Paul Dirac, The Principles of Quantum Mechanics (1947)
Space—Time—Matter (1952)

(Hudson Taylor’s Choice Sayings: A Compilation from His Writings and Addresses. London: China Inland Mission, n.d., 49).
Wisdom and Compassion
Source: Matter and Consciousness, 1984/1988/2013, p. 7
Source: "Some comments on systems and system theory," (1986), p. 1

“We prove what we want to prove, and the real difficulty is to know what we want to prove.”
On prouve tout ce qu'on veut, et la vraie difficulté est de savoir ce qu'on veut prouver.
Système des Beaux-Arts (1920), as quoted in The Most Brilliant Thoughts of All Time (In Two Lines or Less) by John M. Shanahan, p. 34
Variant translation: We prove anything we want to prove, and the real difficulty is to know what we want to prove.
Think Better: An Innovator's Guide to Productive Thinking
Source: 1970s, Ecodynamics: A New Theory Of Societal Evolution, 1978, p. 266 as cited in: " Ecodynamics and societal evolution http://kairos.laetusinpraesens.org/83deval8_8_h_13" at Kairos @ Laetus-in-Praesens.org. Accessed Feb 25, 2012