The pale organisms of literary heroes feeding under the author's supervision swell gradually with the reader's lifeblood; so that the genius of a writer consists in giving them the faculty to adapt themselves to that - not very appetizing - food and thrive on it, sometimes for centuries.
This quote from Vladimir Nabokov's "Despair" suggests that literary characters are almost like living organisms that thrive under the careful guidance of their authors. They gain vitality and substance through the engagement and emotional investment of readers, who provide the necessary nourishment for their growth. The writer's talent lies in enabling these characters to adapt and flourish, even when the material they feed on is not particularly appealing.
Nabokov implies that just as real organisms evolve to survive, literary heroes become vibrant through their interplay with readers over time. This relationship underscores the significance of both the author's craft and the reader's imagination in breathing life into fictional entities, allowing them to endure long after their creation.