Micko

Source: A Moveable Feast (1964), Ch. 2
Context: I would stand and look out over the roofs of Paris and think, "Do not worry. You have always written before and you will write now. All you have to do is write one true sentence. Write the truest sentence you know."

No source in Hemingway's works has been found. May have originated in a 2000 post to the Usenet group alt.support.depression. link https://groups.google.com/forum/#!original/alt.support.depression/wYH4aCNHyp4/_d50yuXTeHsJ
Disputed

Variant: There's nothing to writing. All you do is sit down at a typewriter and open a vein.

NBC interview (1987)

Source: On the Road: the Original Scroll

Source: The Dharma Bums

In the loneliness of my life, my father dead, my brother dead, my mother far away, my sister and my wife far away, nothing here but my own tragic hands that once were guarded by a world, a sweet attention, that now are left to guide and disappear their own way into the common dark of all our death, sleeping in me raw bed, alone and stupid...
Visions of Cody (1960)

The Dharma Bums (1958)

The Town and the City (1950)
Context: He saw that all the struggles of life were incessant, laborious, painful, that nothing was done quickly, without labor, that it had to undergo a thousand fondlings, revisings, moldings, addings, removings, graftings, tearings, correctings, smoothings, rebuildings, reconsiderings, nailings, tackings, chippings, hammerings, hoistings, connectings — all the poor fumbling uncertain incompletions of human endeavor. They went on forever and were forever incomplete, far from perfect, refined, or smooth, full of terrible memories of failure and fears of failure, yet, in the way of things, somehow noble, complete, and shining in the end. This he could sense even from the old house they lived in, with its solidly built walls and floors that held together like rock: some man, possibly an angry pessimistic man, had built the house long ago, but the house stood, and his anger and pessimism and irritable labourious sweats were forgotten; the house stood, and other men lived in it and were sheltered well in it.

Source: On the Road: The Original Scroll

Not a Kerouac quote, but by Jon Krakauer, from his nonfiction book Into the Wild (1996).
Misattributed
Source: On the Road

This is not a quote by Kerouac. It's a quote by CBS broadcaster Charles Kuralt who used to present a TV news segment called 'On the Road' (which is probably how the confusion arose). This particular statement by Kuralt was made in May 1996 to students of Skidmore College, Saratoga Springs, New York: http://news.google.com/newspapers?nid=1298&dat=19960527&id=yf8yAAAAIBAJ&sjid=yQcGAAAAIBAJ&pg=3106,5606314
Misattributed

Misattributed
Source: Often attributed to Kerouac's On the Road, the quote cannot be found in that book, nor in any of Kerouac's other published works.