For it is mutual trust, even more than mutual interest that holds human associations together. Our friends seldom profit us but they make us feel safe.

—H. L. Mencken

A few years ago, in the early days of the blogging phenomenon, a New York–based web designer named Jason Kottke told a fascinating story on his blog,, about his experience with a coffee-and-doughnuts street vendor he called Ralph.

“I stepped up to the window, ordered a glazed donut (75 cents),” Kottke writes, “and when he handed it to me, I handed a dollar bill back through the window. Ralph motioned to the pile of change scattered on the counter and hurried on to the next customer, yelling ‘Next!’ over my shoulder. I put the bill down and grabbed a quarter from the pile.” Kottke was intrigued by this behavior, so he decided to investigate. “I walked a few steps away and turned around to watch the interaction between this business and its customers. For five minutes, everyone either threw down exact change or made their own change without any notice from Ralph; he was just too busy pouring coffee or retrieving crullers to pay any attention to the money situation.”1

As he observed and considered what may be gained or lost by this unusual policy, Kottke noticed that Ralph was serving an extraordinary number of customers. To confirm this suspicion, he went and watched two other similar vendors nearby. On average, both spent twice as much time with each customer and served half as many in a ...

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