Sontag identifies something that goes beyond the familiar notion that readers become writers: she's saying that writing itself is fundamentally *reactive*, born from the specific encounter with someone else's words rather than springing from pure inspiration or lived experience alone. This matters because it challenges the romantic myth of the solitary genius and reveals that even our most original thoughts are conversations with what we've already absorbed. A journalist who finally sits down to write an investigation, for instance, often does so because a single article or book lit a match—not because she simply accumulated enough facts, but because reading another's voice showed her what was possible to say and how to say it. The insight cuts against the grain of self-help culture that treats reading and writing as separate pursuits, when they're actually locked in an intimate dance.