What are you doing? Users of Twitter answer that question all day long. Here is Twitter’s inquisitor, Evan Williams. He’s posing for his picture in a magazine. Credit: Toby Burditt

When he was 16, Evan Williams loved reading business books. The first one he read was about real estate, and at the time, he lived in Clarks, a town in central Nebraska that today has a population of 379 and a median home value of $34,900. Williams wasn't particularly interested in investing in property in Clarks or anywhere else, but he reveled in the fact that it was so easy to learn about building businesses and making money. "I realized I could go buy books and learn something that people had spent years learning about," he recalls. "I was very intrigued with the idea that there's all this stuff out there to know that you could use to your advantage. It was written down in these books, and no one around me was using it."

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