“Of course the illusion of art is to make one believe that great literature is very close to life, but exactly the opposite is true. Life is amorphous, literature is formal.”

Source: The Book of Disquiet

Literature and Revolution (1924), edited by William Keach (2005), Ch. 4 : Futurism, p. 120
Variants:
Art is not a mirror to hold up to society, but a hammer with which to shape it.
Remarks apparently derived from Trotsky's observations, or those he implies preceded his own, this is attributed to Bertolt Brecht in Paulo Freire : A Critical Encounter (1993) by Peter McLaren and Peter Leonard, p. 80, and to Vladimir Mayakovsky in The Political Psyche (1993) by Andrew Samuels, p. 9
Art is not a mirror held up to society, but a hammer with which to shape it.
Context: Art, it is said, is not a mirror, but a hammer: it does not reflect, it shapes. But at present even the handling of a hammer is taught with the help of a mirror, a sensitive film that records all the movements. Photography and motion-picture photography, owing to their passive accuracy of depiction, are becoming important educational instruments in the field of labor. If one cannot get along without a mirror, even in shaving oneself, how can one reconstruct oneself or one's life, without seeing oneself in the "mirror" of literature? Of course no one speaks about an exact mirror. No one even thinks of asking the new literature to have mirror-like impassivity. The deeper literature is, and the more it is imbued with the desire to shape life, the more significantly and dynamically it will be able to "picture" life.

Source: The Meaning of Culture (1929), p. 175

Source: Our Lady of Darkness (1977), Chapter 27 (p. 166)

From a speech entitled Come September http://ada.evergreen.edu/~arunc/texts/politics/comeSeptember.pdf.
Speeches

Source: The Cream of the Jest (1917), Ch. 27 : Evolution of a Vestryman
Context: The purblind majority quite honestly believed that literature was meant to mimic human life, and that it did so. And in consequence, their love-affairs, their maxims, their so-called natural ties and instincts, and above all, their wickedness, became just so many bungling plagiarisms from something they had read, in a novel or a Bible or a poem or a newspaper. People progressed from the kindergarten to the cemetery assuming that their emotion at every crisis was what books taught them was the appropriate emotion, and without noticing that it was in reality something quite different. Human life was a distorting tarnished mirror held up to literature: this much at least of Wilde's old paradox — that life mimicked art — was indisputable. Human life, very clumsily, tried to reproduce the printed word.

Section 4.5 <!-- p. 202 -->
The Crosswicks Journal, A Circle of Quiet (1972)