„Unless we make revolutionary reforms, some day — in some unknown serra — some unknown Fidel Castro will rise up in Brazil.“

„We, in some unknown Power's employ,
Move on a rigorous line“

—  Matthew Arnold English poet and cultural critic who worked as an inspector of schools 1822 - 1888

"Stanzas in Memory of the Author of "Obermann"" (1852), st. 34
Contexto: We, in some unknown Power's employ,
Move on a rigorous line;
Can neither, when we will, enjoy,
Nor, when we will, resign.

„He must create, must pour out creation. By some strange, unknown, inward urgency he is not really alive unless he is creating.“

—  Pearl S. Buck American writer 1892 - 1973

As quoted in The 101 Habits of Highly Successful Screenwriters: Insiders Secrets from Hollywood's Top Writers (2001) by Karl Inglesias, p. 4. This has also appeared on the internet in several slightly paraphrased forms.
Contexto: The truly creative mind in any field is no more than this: a human creature born abnormally, inhumanly sensitive. To him, a touch is a blow, a sound is a noise, a misfortune is a tragedy, a joy is an ecstasy, a friend is a lover, a lover is a god, and failure is death. Add to this cruelly delicate organism the overpowering necessity to create, create, create — so that without the creating of music or poetry or books or buildings or something of meaning, his very breath is cut off from him. He must create, must pour out creation. By some strange, unknown, inward urgency he is not really alive unless he is creating.

„Some speak of things we know, as new;
And you, of things unknown as things forgot.“

—  Marianne Moore American poet and writer 1887 - 1972

"Quoting an Also Private Thought" (this poem is a very slight reworking of an earlier poem "As Has Been Said")

„More is happening out there than we are aware of.
It is possibly due to some unknown direful circumstance.“

—  Edward Gorey American writer, artist, and illustrator 1925 - 2000

„Fidel Castro is dead!“

—  Donald J. Trump 45th President of the United States of America 1946

Tweet https://twitter.com/realDonaldTrump/status/802499192237080576 mentioning Castro's death (26 November 2016)
2010s, 2016, November

„For some unknown reason, success usually occurs in private, while failure occurs in
full view.“

—  Jill Shalvis American writer 1963

Fonte: The Sweetest Thing

„No one is so accursed by fate,
No one so utterly desolate,
But some heart, though unknown,
Responds unto his own.“

—  Henry Wadsworth Longfellow American poet 1807 - 1882

Endymion, st. 8 (1842).

„Knowledge must start from some foundation, something must be recognized as known; otherwise we shall be obliged always to define one unknown by means of another.“

—  P. D. Ouspensky, livro Tertium Organum

Fonte: Tertium Organum (1912; 1922), Ch. I
Contexto: The most difficult thing is to know what we do know, and what we do not know.
Therefore, desiring to know anything, we shall before all else determine WHAT we accept as given, and WHAT as demanding definition and proof; that is, determine WHAT we know already, and WHAT we wish to know.
In relation to the knowledge of the world and of ourselves, the conditions would be ideal could we venture to accept nothing as given, and count all as demanding definition and proof. In other words, it would be best to assume that we know nothing, and make this our point of departure.
But unfortunately such conditions are impossible to create. Knowledge must start from some foundation, something must be recognized as known; otherwise we shall be obliged always to define one unknown by means of another.

„The Spirit tells me - Fidel Castro will die - in the 90's. Oooh my! Some will try to kill him and they will not succeed. But there will come a change in his physical health, and he will not stay in power, and Cuba will be visited of God.“

—  Benny Hinn American-Canadian evangelist 1952

[The Underground Christian Network, "Benny Hinn and Beyond: Word Faith movements hidden agenda: The Joker, The Guru and the Jack of Spades" http://www.sermonaudio.com/sermoninfo.asp?SID=420067844, CD Edition 1 of 2, SermonAudio.com, 2006-04-21]

„The hill-cat boasts some cunning of her own,
Some stealthy tricks to better beasts unknown
That quick with prey enough her hunger blunts
And feeds her fat while gaunt the lion hunts.“

—  Robert Browning, livro Sordello

Book the First
Sordello (1840)

„It was not his fight. Not personally his fight. No more his fight than any one of them. But he had made it his. Because of Stone, because of Rand and Harriet, because of priest who’d hounded him across half the continent, he had tried to make a fight of it. And perhaps, as well, because of something undefinable, unknown to himself, unsuspected in himself—some crazy idealism, some deep-rooted sense of justice, some basic aversion to bullies and bigots and reformers.“

—  Clifford D. Simak, livro Time is the Simplest Thing

Fonte: Time is the Simplest Thing (1961), Chapter 32 (p. 245)

„Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns — the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones.
The absence of evidence is not evidence of absence, or vice versa.“

—  Donald Rumsfeld U.S. Secretary of Defense 1932

Department of Defense news briefing (12 February 2002)
Variant:
Now what is the message there? The message is that there are no "knowns." There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know. So when we do the best we can and we pull all this information together, and we then say well that's basically what we see as the situation, that is really only the known knowns and the known unknowns. And each year, we discover a few more of those unknown unknowns.
:It sounds like a riddle. It isn't a riddle. It is a very serious, important matter.
:There's another way to phrase that and that is that the absence of evidence is not evidence of absence. It is basically saying the same thing in a different way. Simply because you do not have evidence that something exists does not mean that you have evidence that it doesn't exist. And yet almost always, when we make our threat assessments, when we look at the world, we end up basing it on the first two pieces of that puzzle, rather than all three.
:* Extending on his earlier comments in a press conference at NATO Headquarters, Brussels, Belgium (6 June 2002) http://www.nato.int/docu/speech/2002/s020606g.htm
2000s

„It feels like my soul is slowly leaving my body and heading off to an unknown place, some "safe" place where it doesn't have to put up with me and my night terrors.“

—  Paulo Coelho, livro Adultério

Fonte: Adultery

„Some rise by sin, and some by virtues fall.“

—  William Shakespeare English playwright and poet 1564 - 1616

„The present has its élan because it is always on the edge of the unknown and one misunderstands the past unless one remembers that this unknown was once part of its nature.“

—  V.S. Pritchett British writer and critic 1900 - 1997

"Boris Pasternak: Unsafe Conduct", p. 14
The Myth Makers: European and Latin American Writers (1979)

„Time will pass; these mood will pass; and I will, eventually, be myself again. But then, at some unknown time, the electrifying carnival will come back into my mind.“

—  Kay Redfield Jamison American bipolar disorder researcher 1946

Fonte: An Unquiet Mind: A Memoir of Moods and Madness

„So at the end of this day, we give thanks
For being betrothed to the unknown.“

—  John O'Donohue Irish writer, priest and philosopher 1956 - 2008

„We are to-day in the midst of a revolutionary epoch fully as thorough as that of the Renaissance and Reformation.“

—  Walter Rauschenbusch United States Baptist theologian 1861 - 1918

Fonte: Christianity and the Social Crisis (1907), Ch.2 The Social Aims of Jesus, p. 45
Contexto: We are to-day in the midst of a revolutionary epoch fully as thorough as that of the Renaissance and Reformation. It is accompanied by a reinterpretation of nature and of history. The social movement has helped to create the modern study of history. Where we used to see a panorama of wars and strutting kings and court harlots, we now see the struggle of the people to wrest a living from nature and to shake off their oppressors. The new present has created a new past. The French Revolution was the birth of modern democracy, and also of the modern school of history.

„Man can learn nothing unless he proceeds from the known to the unknown.“

—  Claude Bernard French physiologist 1813 - 1878

Bulletin of New York Academy of Medicine, Vol. IV (1928)