“The hard part is discriminating between factual reporting and journalistic fiction. Last year at the National Press Club I said out loud and in public [C-SPAN was there] that the difference between me and a lot of reporters is that I do good fiction. Some were polite enough to chuckle.”

Facebook Nation: Total Information Awareness (2nd Edition), 2014

Interview with Weird Tales (24 May 2007) http://weirdtales.net/wordpress/2007/05/24/george-rr-martin-on-magic-vs-science/
Context: I think that for science fiction, fantasy, and even horror to some extent, the differences are skin-deep. I know there are elements in the field, particularly in science fiction, who feel that the differences are very profound, but I do not agree with that analysis. I think for me it is a matter of the furnishings. An elf or an alien may in some ways fulfill the same function, as a literary trope. It’s almost a matter of flavor. The ice cream can be chocolate or it can be strawberry, but it’s still ice cream. The real difference, to my mind, is between romantic fiction, which all these genres are a part of, and mimetic fiction, or naturalistic fiction.

Opening address to the Pacific Regional Media Training Workshop on "Women's Issues, Women's Voices," January 2005

Attributed to an interview on Larry King Live; also quoted in Quotable Quotes (1997) edited by Deborah Deford
Attributed variant: The difference between fiction and reality is that fiction has to make sense.
Clancy here expresses an idea evoked in similar statements made by others, all derived from the orignial made by Lord Byron:
Lord Byron: Truth is always strange; stranger than fiction.
Mark Twain: Truth is stranger than fiction, but it is because fiction is obliged to stick to possibilities, truth isn't.
G. K. Chesterton: Truth must necessarily be stranger than fiction, for fiction is the creation of the human mind and therefore congenial to it.
Leo Rosten: Truth is stranger than fiction; fiction has to make sense. (attributed)
1990s

Writing and Being (1991)
Context: I have said that nothing factual that I write or say will be as truthful as my fiction. The life, the opinions, are not the work, for it is in the tension between standing apart and being involved that the imagination transforms both. Let me give some minimal account of myself. I am what I suppose would be called a natural writer. I did not make any decision to become one. I did not, at the beginning, expect to earn a living by being read. I wrote as a child out of the joy of apprehending life through my senses — the look and scent and feel of things; and soon out of the emotions that puzzled me or raged within me and which took form, found some enlightenment, solace and delight, shaped in the written word.

On his writing preferences in “An Interview with Luis J. Rodriguez” https://www.epl.org/an-interview-with-luis-j-rodriguez-2/ (Evanston Public Library; 2011)

The History of Freedom in Christianity (1877)
Context: That men should understand that governments do not exist by divine right, and that arbitrary government is the violation of divine right, was no doubt the medicine suited to the malady under which Europe languished. But although the knowledge of this truth might become an element of salutary destruction, it could give little aid to progress and reform. Resistance to tyranny implied no faculty of constructing a legal government in its place. Tyburn tree may be a useful thing; but it is better still that the offender should live for repentance and reformation. The principles which discriminate in politics between good and evil, and make states worthy to last, were not yet found.