[T]he idea is that we should all write the story of the Moonstone in turn—as far as our own personal experience extends, and no farther.
This quotation comes at the beginning of Chapter I, First Period, and is the instruction received by Gabriel Betteredge from Franklin Blake regarding the project of assembling narratives about the Moonstone. The language Franklin uses here is explicitly setting up each of the narratives as subjective ("our own personal experience")—a classification which rings true. Each narrative offers us the subjective opinions and viewpoints of the narrator, and we must sift through this to arrive at the objective matter—the facts and events—of the narrative. Blake's vision of each narrator telling the story "in turn" also proves true. The Moonstone does not feature disparate narrators each giving their version of the same set of events. Instead, each narrator picks up where the last left off—The Moonstone offers a variety of narrative voices, not of plot.