Economists focus on the problem of scarcity—on how people allocate their resources (including both time and money) in the face of many competing demands. In their extraordinarily illuminating book, the behavioral economist Sendhil Mullainathan and the cognitive psychologist Eldar Shafir explore something quite different, which is the feeling of scarcity, and the psychological and behavioral consequences of that feeling. They know that the feeling of scarcity differs across various kinds of experiences and that people can feel “poor” with respect to money, time, or relationships with others.But their striking claim, based on careful empirical research, is that across all of those categories, the feeling of scarcity has quite similar effects. It puts people in a kind of cognitive tunnel, limiting what they are able to see. It depletes their self-control. It makes them more impulsive and sometimes a bit dumb. What we often consider a part of people’s basic character—an inability to learn, a propensity to anger or impatience—may well be a product of their feeling of scarcity. If any of us were similarly situated, we might end up with a character a lot like theirs. An insidious problem is that scarcity produces more scarcity. It creates its own trap.Because they lack money, poor people must focus intensely on the economic consequences of expenditures that wealthy people consider trivial and not worth worrying over. Those without a lot of time have to hoard their minutes, and they may have trouble planning for the long term. The cash-poor and the time-poor have much in common with lonely people, for whom relationships with others are scarce. When people struggle with scarcity, their minds are intensely occupied, even taken over, by what they lack.