“It's an old saying that one still has to know something, despite everything.”

Source: Dandelion Wine (1957), p. 142
Context: “I don’t know,” he admitted.
“Well.” She started pouring tea. “To start things off, what do you think of the world?”
“I don’t know anything.”
“The beginning of wisdom, as they say. When you’re seventeen you know everything. When you’re twenty-seven if you still know everything you’re still seventeen.”
“You seem to have learned quite a lot over the years.”
“It is the privilege of old people to seem to know everything. But it’s an act and a mask, like every other act and mask. Between ourselves, we old ones wink at each other and smile, saying, How do you like my mask, my act, my certainty? Isn’t life a play? Don’t I play it well?”
They both laughed quietly.

The Old Men Admiring Themselves In The Water http://poetry.poetryx.com/poems/1663/
In The Seven Woods (1904)
Context: I heard the old, old men say,
'Everything alters,
And one by one we drop away.'
They had hands like claws, and their knees
Were twisted like the old thorn-trees
By the waters.
I heard the old, old men say,
'All that's beautiful drifts away
Like the waters.

Vatican Nuncio in Holy Land appeals for dialogue to end Israel-Gaza conflict http://www.archivioradiovaticana.va/storico/2014/07/21/vatican_nuncio_in_holy_land_appeals_for_dialogue_to_end_israel-gaza/en-1103193 (21 July 2014)

Source: Podkayne of Mars (1963), Chapter 5 (p. 50)

On meeting Carl Barat, The Guardian, January 2003.
Carl Barat

Edward Everett Hale in a statement published in A Year of Beautiful Thoughts‎ (1902) by Jeanie Ashley Bates Greenough, p. 172; <!-- and perhaps as early as an edition of Ten Times One is Ten (1870) by Hale--> This has been misattributed to Keller in published works since at least 1980. Keller and Hale were good friends, and letters to Hale can be found in her youthful autobiography The Story of My Life (1902). In 1910 Keller dedicated her poem "The Song of the Stone Wall" to Hale who had died in 1909.
Misattributed
Variant: I am only one, but I am one. I can not do everything, but I can do something. I must not fail to do the something that I can do.

Statement published in A Year of Beautiful Thoughts‎ (1902) by Jeanie Ashley Bates Greenough, p. 172, Third statement for June 11. This has often been misattributed to Helen Keller in some published works since at least 1980, perhaps because she somewhere quoted it.
Variant:
I am only one,
But still I am one.
I cannot do everything,
But still I can do something;
And because I cannot do everything,
I will not refuse to do the something that I can do.
The Book of Good Cheer : A Little Bundle of Cheery Thoughts‎ (1909) by Edwin Osgood Grover, p. 28; also in Masterpieces of Religious Verse (1948) by James Dalton Morrison, p. 416, where it is titled "Lend a Hand"
Variant: I am only one, but still I am one. I cannot do everything, but still I can do something; and because I cannot do everything, I will not refuse to do something that I can do.

The Rickover Effect (1992)
Context: Everything new endangers something old. A new machine replaces human hands; a new source of power threatens old businesses; a new trade route wipes out the supremacy of old ports and brings prosperity to new ones. This is the price that must be paid for progress and it is worth it.

Review of Their Finest Hour by Winston Churchill, New Leader (14 May 1949)
Context: It is difficult for a statesman who still has a political future to reveal everything that he knows: and in a profession in which one is a baby at 50 and middle-aged at seventy-five, it is natural that anyone who has not actually been disgraced should feel that he still has a future.