It is so fundamental to our development and so critical to proper functioning that, in adults, its absence can signal a grave problem. An important 2004 study makes that plain. A team of cognitive scientists organized a simple gambling game in which participants had to choose one of two computerized roulette-style wheels to spin. Depending on where the arrow landed on their chosen wheel, they would either win money or lose money. When participants spun a wheel and lost money, they felt bad. No surprise. But when they spun a wheel, lost money, and learned that if they’d chosen the other wheel,
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