Monkeys can teach us a lot about economics. Their brains and emotions are very similar to ours. As fellow mammals, monkeys and humans both develop strong emotions that govern our lives, our society and our economy.

In the early 1990s, a team of psychologists set out to determine how a mother's attentiveness affects her children as they grow up. They took two groups of monkeys and placed them in two different environments. In the first environment, the mother always had access to food. She could focus all her attention on her baby instead of constantly looking for food. In the second environment, the food was harder to find. The mother had to spend so much time looking for food she often neglected her child.

The results were tragic. The second group of babies grew up with noticeable despair and anxiety issues. Their brains literally looked different. Their brain cells couldn't regulate emotions like their healthier peers'. Once they became adults, the second group of monkeys was shy, clingy, weak and socially awkward. They had trouble making friends, and they never became leaders. They were forever scarred—and their potential forever stunted—by their distracted mothers.

In a way, the same experiment is taking place in American society today. Some mothers have easy access to the basic necessities of life —food, shelter, clothing, transportation, healthcare—but many do not. Millions of mothers live paycheck to paycheck, working multiple jobs and long hours, leaving them too busy and too exhausted to give their children the same attention as their wealthier peers.

The difference is so drastic that children raised in poverty have brain activity that looks like it's been damaged by a stroke. Study after study show that these early scars last long into adulthood, affecting everything from job prospects to marital happiness.

It would be cruel and illogical to argue that these children are responsible for their lot in life, but every time I write about income inequality, that's exactly what I hear. "I strongly disagree with your statement that more people 'deserve' the opportunity to succeed," one reader told me recently. "Success is in everyone's face. One has to reach out and grab it."

But clearly not everyone is staring success in the face after childhood. In fact, many children are raised not to reach out and grab it.

Psychologists have spent decades studying the different attitudes people develop by living in different social classes. According to a recent article in the Annual Review of Psychology, they've come to some striking conclusions.

First, higher-income parents encourage their children to follow their dreams. They encourage critical thinking and support expression of likes, dislikes, feelings, and thoughts, and then give them opportunities to pursue those interests. Lower-income parents tend to emphasize toughness and pride in the face of adversity. They emphasize rules that must not be broken, and then let the children figure out the rest on their own.

From there, the children go to school, where higher-income children are given opportunities to work independently, think creatively and ask questions. Their parents take an active role, challenging practices that they disagree with. Their teachers treat them like adults and reward students who speak up and take initiative.

Lower-income children usually find themselves in a more regimented environment. They walk through metal detectors and aren't trusted with basic classroom equipment. Their parents want to be involved, but they don't assert themselves. Their teachers demand respect and reward students who show deference.

By the time they enter the workforce, it isn't hard to see how these two groups have been ingrained with two different attitudes toward success. The higher-income children have learned leadership skills like taking initiative, treating authorities as equals, and thinking outside the box, while their lower-income peers have learned to keep their heads down and do only what they're told.

For those Americans who have been materially successful, it may seem like everyone else simply chose not to follow the same path, but the reality is that most Americans don't know how to find that path. And in the greatest tragedy of all, for many Americans in today's economy, the path may not even exist as long as they live.