“I do not evolve, I AM.”

Tuesdays with Morrie (1997)

Green Eggs and Ham (1960)

Quoted in "Epistle to Casualanus", XXXVI, section 32, by St. Augustine; translation by J.G. Cunningham
Context: When I am here I do not fast on Saturday; but when I am at Rome I do: whatever church you may come to, conform to its custom, if you would avoid either receiving or giving offense.

Source: Leaves of Grass

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"

In an interview in the New York Times (16 December 1957), cited in a footnote on page 32 of "Work, Society, and Culture" by Yves Reni Marie Simon, and also in a footnote (in German) on page 360 of "Vita activa oder Vom taetigen Leben" by Hannah Arend (1981)

Variants:

Basic research is when I'm doing what I don't know I'm doing.

Research is what I'm doing when I don't know what I'm doing.

Basic research is what I am doing when I don't know what I am doing.

"From tail to tale on the path of pilgrims in life" http://news.scotsman.com/scitech.cfm?id=374772005, The Scotsman ()