Former Posting: footnote - I tried to find another related quote (namely, the full paragraph for “"In a first-rate piece of fiction, the real clash is not between the characters, but between the author and the world")…and got to an information which might be useful here …“An interesting related topic to the difficulty of mingling souls in Nabokov’s fiction is Stephen Blackwell’s discussion of the “interpenetration of souls” that is the ideal “author-reader interaction,” an idea that Blackwell argues is shared by Nabokov and Iulii Aikhenvald.” (Blackwell 29-36). Footnote to ch.12, p.191 in “Nabokov’s Permanent Mystery: The Expression of Metaphysics in His Work” by David S. Rutledge.

Present Posting: “In the third section of chapter 14 of Speak, Memory ...Nabokov reminds us that ‘competition in chess problems is not really between White and Black but between the composer and the hypothetical solver (just as in a first-rate work of fiction the real clash is not  between the characters but between the author and the world’).
In Autobiographical Statements in Twentieth-Century Russian Literature by Jane Gary Harris