Advertising was indeed Winfrey's main revenue source, and when she sold her audiences she was delivering not mere eyeballs but minds whose buying decisions had been conditioned by her unusually strong influence, which eventually "exceed[ed] that of any other celebrity—perhaps in history," according to Craig Garthwaite of Northwestern's Kellogg School of Management. It did not happen overnight, however. As one biographer writes, Winfrey was an enthusiastic shopper, and "for years she had shared her spending orgies with her viewers—her towels, her pajamas, her cashmere sweaters, her diamond earrings." As time went on, her enthusiasm would morph into quasi-endorsements of particular products, her magical touch performing little miracles for small companies. To take one minor example, there was the firm named LightWedge, maker of a reading light; when Oprah said on air, "I need to get one of those," the little company booked $90,000 in sales in a single afternoon.

Tim Wu, The Attention Merchants, loc. 797