Some of Mr. Shafir’s work, described with the Harvard economist Sendhil Mullainathan in the book “Scarcity,” suggests that poverty consumes much of the cognitive bandwidth we need to be successful at other life tasks. In experiments, they’ve shown that people who are asked to think about financial problems — or who experience financial strain — perform worse on spatial and reasoning tasks. Poverty, they argue, exacts a mental tax akin to lowering a person’s IQ.

And those mental costs have a way of reinforcing poverty. If you’re worried about eviction, you may forget a doctor’s appointment; if you’re preoccupied with how to pay the bills, you may be worse at making other decisions. That is a very different thing, however, from saying that people who don’t have the right attitude remain poor.

Mr. Evans’s work suggests that the kind of chronic stress experienced by many children growing up in poverty may damage the parts of the brain where researchers believe functions like working memory reside.

Other related research disputes the idea that public assistance undermines attributes like motivation, another common argument of welfare critics like Paul Ryan and Mr. Carson (he has also said that public housing shouldn’t be too comfortable, lest it induce long-term dependency). Studies of the poor have consistently shown that income much more strongly predicts life outcomes like educational attainment than time spent on welfare does.

Yet another strand of evidence says that the context of where people live, well beyond stressful environments in their homes or neighborhoods, shapes their chances of escaping poverty. One large recent study, led by the Stanford economist Raj Chetty, showed that poor children face very different odds of scaling the income ladder — of achieving the Ben Carson story — depending on where they grow up. Poor children in Montgomery, Ala., for example, are less likely than poor children in San Francisco to reach the middle and upper class as adults.

Looking at an interactive Upshot map done in conjunction with Mr. Chetty, it’s hard to argue that the “right mind-set” is what really matters. “It just so happens that everybody born in Montgomery has the wrong attitude?” Mr. Shafir said. “That’s just absurd.”