Quotes about difficulty
page 9
Source: The Romantic Generation (1995), Ch. 6 : Chopin: Virtuosity Transformed
Source: Cognitive Psychology, 1967, p. 94

Shri K. R. Narayanan President of India in Conversation with N. Ram on Doordarshan and All India Radio

Source: The Cambridge Encyclopedia of the English Language, 1987, p. 371

“The difficulty is that we try to perfect others before we perfect ourselves.”
Words of Wisdom (2010)

Opening address to the National Day of Prayer in Suva, 15 May 2005 (excerpts) http://www.fiji.gov.fj/publish/page_4607.shtml
Source: The architecture of markets, 2001, p. 16
"Moral Beliefs"
Source: An Invitation to Quantum Field Theory (2012), Ch. 1 : Why Do We Need Quantum Field Theory After All?
Descent into Hell (1937), Ch. 5, "Return to Eden"

Introduction
Small Houses: Their Economic Design and Construction (1922)
Kenneth Boulding, 1973, p. 21 as cited in: Donald W. Cole (1983) Conflict resolution technology. p. 5
1970s

Alfred Binet (1900), La suggestibilite, Paris: Schleicher. p. 119–120); As cited in: Carson (1999, 363-4)

1910s, Address to Congress: Analyzing German and Austrian Peace Utterances (1918)

2010s, Democracy Now! interview (2011)

Memo (May 30, 1942) to the Chief of Combined Operations on the design of floating piers (which later became Mulberry Harbours) for use on landing beaches; in The Second World War, Volume V : Closing the Ring (1952) Chapter 4 (Westward Ho! Synthetic Harbours).
Post-war years (1945–1955)

Spencer here references William Benjamin Carpenter, Principles of Comparative Physiology http://books.google.com/books?id=ovgEAAAAYAAJ& see p. 473
The Development Hypothesis (1852)

Edward Hall Alderson, counsel employed in opposition to the proposed Liverpool & Manchester Railway. On 25th April, 1825, George Stephenson gave evidence to the House of Commons committee looking into the proposed railway.

Source: On the Study and Difficulties of Mathematics (1831), Ch. I.

Speech in Limehouse, East London (30 July 1909), quoted in Better Times: Speeches by the Right Hon. D. Lloyd George, M.P., Chancellor of the Exchequer (London: Hodder & Stoughton, 1910), p. 156.
Chancellor of the Exchequer
(1986) n.p.
Structures are no longer valid', in "Ein Gespräch..."

Progress, Coexistence and Intellectual Freedom (1968), Dangers, International Tensions And New Principles

" Do you have problems in life? Watch This! by Mufti Menk https://www.youtube.com/watch?v=wgp2zbE9Ofg", YouTube (2013)
Lectures

2000s, 2003, Remarks after Columbia space shuttle disaster (February 2003)

“Nature laughs at the difficulties of integration.”
Quoted in I. Gordon and S. Sorkin, The Armchair Science Reader, New York, 1959.

1840s, Past and Present (1843)

Letter to his future wife, Maria Bicknell (26 August 1816), as quoted in Leslie Parris and Ian Fleming-Williams, Constable (Tate Gallery Publications, London, 1993), p. 119
1800s - 1810s

Letter to Henry Ashworth (21 July 1848), quoted in John Morley, The Life of Richard Cobden (London: T. Fisher Unwin, 1905), p. 488.
1840s

" Come up higher!"
Reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 564.

Report on the Theory of Numbers (1859) Part I, pp. 56-57.
The Collected Mathematical Papers of Henry John Stephen Smith (1894) Vol. 1
What is Knowledge? (1971)
Book 4, § 44.
Life of Apollonius of Tyana

Speech at the annual dinner of The Royal Society of St. George (6 May 1924), quoted in On England, and Other Addresses (1926), pp. 3-4.
1924

Speech http://www.bartleby.com/349/authors/133.html to the electors at Edinburgh (May 1839)

Source: Think Big (1996), p. 206

Daniel Bedingham, Detlef Dürr, GianCarlo Ghirardi, Sheldon Goldstein, Roderich Tumulka, Nino Zanghì, "Matter Density and Relativistic Models of Wave Function Collapse", J Stat Phys (2014) 154:623–631
The Ayodhya temple-mosque dispute: Focus on Muslim sources (1993)

Un Art de Vivre (The Art of Living) (1939), The Art of Growing Old

Source: Reasonable Faith: Christian Truth and Apologetics (1994), pp. 35-36.

1920s, Ordered Liberty and World Peace (1924)

Source: The Income Tax: Root of All Evil (1954), p. 43

Source: The Mind and the Brain, 1907, p. 184
Known as the Sermon of ash-Shiqshiqiyyah (roar of the camel), It is said that when Amir al-mu'minin reached here in his sermon a man of Iraq stood up and handed him over a writing. Amir al-mu'minin began looking at it, when Ibn `Abbas said, "O' Amir al-mu'minin, I wish you resumed your Sermon from where you broke it." Thereupon he replied, "O' Ibn `Abbas it was like the foam of a Camel which gushed out but subsided." Ibn `Abbas says that he never grieved over any utterance as he did over this one because Amir al-mu'minin could not finish it as he wished to.
Nahj al-Balagha

As quoted in Anecdotes, Observations, and Characters, of Books and Men (1820) by Joseph Spence [published from the original papers; with notes, and a life of the author, by Samuel Weller Singer]; "Spence's Anecdotes", Section IV. pp. 134–136.
Attributed

Speech in Conway (c. late July 1892) after the 1892 general election, quoted in Thomas Jones, Lloyd George (London: Oxford University Press, 1951), pp. 16-17.
Backbench MP

in conversation with W.C. Seitz
Quote from Abstract Expressionist Painting in America, W.C, Seitz, Cambridge Massachusetts, 1983, p. 121.
1980's

“God does not care about our mathematical difficulties. He integrates empirically.”
Attributed to Einstein by his colleague Léopold Infeld in his book Quest: An Autobiography (1949), p. 279 http://books.google.com/books?id=fsvXYpOSowkC&lpg=PP1&pg=PA279#v=onepage&q&f=false
Attributed in posthumous publications
Interviewed in Naim Attallah, Singular Encounters (Quartet Books, 1990), p. 136.

Source: Precepts and Judgments (1919), p. 140

"Society, Morality and the Novel" (1957), in The Collected Essays, ed. John F. Callahan (New York: Modern Library, 1995), p. 699.

Speech at a rally at the University Stadium, Lahore (30 October 1947)

1960s
Robert Heller (1975) "Research in light of a dark tunnel" Audit AGB research. London, Spring 1973: Cited in Peter M. Chisnall (1977) Effective industrial marketing. p. 91

in 'Undated notes' 1950; as quoted in The Art of Henry Moore, Will Grohmann, Thames and Hudson, London 1960, n.p.
1940 - 1955

"Exclusive: Bryant Jennings: The Man Behind The Gloves" https://hypefreshmag.com/culture/exclusive-bryant-jennings-the-man-behind-the-gloves, interview with Hypefresh Magazine (April 18, 2015).
Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 6.
Lorentz (1991) " A scientist by choice". Speech by acceptance of the Kyoto Prize in 1991, cited in: Kerry Emanuel (2009) [http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/lorenz-edward.pdf Edward Norton Lorenz 1917-2008 http://eaps4.mit.edu/research/Lorenz/Miscellaneous/Scientist_by_Choice.pdf. National Academy of Sciences Biographical Memoir.

"Bisexuality and the Causes of Homosexuality: The Case of the Sambia"

Source: On Paul Samuelson, as quoted in "Subramanian Swamy: Samuelson - A genius who was my guru" http://www.business-standard.com/article/opinion/subramanian-swamy-samuelson-a-genius-who-was-my-guru-109122200056_1.html, Business Standard (22 December 2009)

Charles Boarman, Sr. in a letter to Robert Brent, the mayor of Washington, D.C., asking for a letter of recommendation for his son's application to enlist in the United States Navy (1811)
A Gentlemanly and Honorable Profession: The Creation of the U.S. Naval Officer Corps, 1794-1815 (1991)

Source: Mani Madhava Chakkyar: The Master at Work, K.N. Panikar, Sangeet Natak Akademi New Delhi, 1994

पण्डित लेखनाथ पौड्यालको विषयमा (On the subject of Pandit Lekhnath Paudyal)
The Karezza Method : Or Magnetation, the Art of Connubial Love (1931) Ch. 17 : Karezza the Beautifier http://www.reuniting.info/karezza_method_lloyd/karezza_the_beautiful

Quote from Turner's letter 4 Dec. 1848 to James Astbury Hammersley; as cited in The life of J.M.W. Turner, Volume II, George Walter Thornbury; Hurst and Blackett Publishers, London, 1862, pp. 115-16
James Astbury Hammersley, himself an artist and art-teacher, wrote Turner to ask him to give his son further instructions in painting
1821 - 1851

Speech in Liverpool (27 October 1903), quoted in The Times (28 October 1903), p. 6.
1900s

Speech to the Economic Students' Union at the School of Economics and Political Science, London (14 December 1900), quoted in The Times (17 December 1900), p. 13.
1900s

"Ten Variable Stars of the Algol Type" http://books.google.com/books?id=UkdWAAAAYAAJ&pg=PA87 (1908) Annals of the Astronomical Observatory of Harvard College Vol.60. No.5

Speech to delegates of the Ulster Unionist Council in Belfast, 3 September 1914.

Source: An Essay on Aristocratic Radicalism (1889), pp. 25-26

Source: Kinski Uncut : The Autobiography of Klaus Kinski (1996), p. 222

Jeremy Irons: power player
The Telegraph
2008-03-13
Chloe
Fox
http://www.telegraph.co.uk/culture/3671865/Jeremy-Irons-Power-player.html
2011-08-11

“Difficulty is as needful to appreciation as labour is to existence.”
No.5. The Antiquary— MISS WARDOUR.
Literary Remains

Source: The Geological Evidences of the Antiquity of Man (1863), Ch.20, p. 386

1820s, Letter to F. Corbin (1820)

Letters to Students: LETTER NO. 92, July, 1918.

On Coalition Government (1945)

Speech http://hansard.millbanksystems.com/commons/1935/may/22/defence-policy in the House of Commons (22 May 1935). This speech reduced the Labour leader George Lansbury to tears (Thomas Jones, A Diary with Letters. 1931-1950 (London: Oxford University Press, 1954), p. 149.)
1935

As quoted in Autobiography and Personal Reminiscences of Major-General Benj. F. Butler https://books.google.com/books?id=0LIBAAAAMAAJ&pg=PA604 (1892), pp. 604–605
Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 451.

Sydpolen (The South Pole) (1912)