For the vast majority of world history, human life—both culture and biology—was shaped by scarcity. Food, clothing, shelter, tools, and pretty much everything else had to be farmed or fabricated, at a very high cost in time and energy. Knowledge was power, and it was hard to come by; for centuries, books had to be copied by hand and were rare and precious. Even people were scarce: Friends and relatives died young (as late as 1900, life expectancy in the United States was approximately 49 years).

This kind of scarcity still rules the world's poorest regions. But in the developed world, hundreds of millions of us now face the bizarre problem of surfeit. Yet our brains, instincts, and socialized behavior are still geared to an environment of lack. The result? Overwhelm—on an unprecedented scale.

"I hate my house," Paula tells me. "It's so overstuffed, I feel like I'm suffocating." Sonya feels the same way about her schedule. "I sprint from one obligation to another," she says. "I feel as if I'm drowning. I can't even connect with the people I love."

Both Paula and Sonya are bright, strong women, more than capable of straightforward tasks like clearing out a room or schedule. Yet when Paula walks into her guest bedroom and Sonya tries to reorganize her time, they sink into a kind of muddled netherworld, like Dorothy in the poppy fields of Oz. Their intentions grow fuzzy. They forget what they're doing. Is this dementia? Alzheimer's? Sheer cussed laziness? None of the above. It's a symptom of overwhelm called attentional blindness. You've almost certainly experienced this, too. Understanding it can help you manage it.