“I am always doing what I cannot do yet, in order to learn how to do it.”

Bio note
Twitter tweets

Variant: And what will I be able to do tomorrow that I cannot yet do today?
Source: Eat, Pray, Love

In debate http://hansard.millbanksystems.com/commons/1952/nov/04/debate-on-the-address in the House of Commons, 4 Nov 1952
Post-war years (1945–1955)
Variant: Personally, I'm always ready to learn, although I do not always like being taught.
Context: Personally, I am always ready to learn, although I do not always like being taught, but I shall not attempt to foreshadow the proposals which will be brought before the House tomorrow. Today it will be sufficient and appropriate to deal with the obvious difficulties and confusion of the situation as we found it on taking office.

Academy of Achievement interview (1991)

Source: The Princess Bride

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.

60 Minutes interview (1998)

Paris Review interview (1986)
Context: I feel that after working a long time, I’ve really learned how to do what I do. I enjoy it. I don’t think there’s anything more satisfying than turning out a good stanza or a good piece of prose. And when you’re satisfied enough, you want to show it to other people. That’s called publication.