On a basic level, it means that if you are born poor you have a higher likelihood of staying poor and dying poor than a person who is born rich, assuming equal levels of intelligence and work ethic. This is not saying it's impossible to make it out of poverty with hard work and luck, it's just that it will take both more work and more luck for the average poor person to attain middle class status than for a rich person to maintain. It's a fairly intuitive idea if you've ever been the least rich in a group of friends. This is not to say it is bad for rich parents to do everything they can for their children, just that their children have an advantage in life.

A rich kid is more likely to go to a private school or a public school with qualified teachers, while the poor student attends an underfunded and underresourced school due to where the family lives. The rich kid's first job is more likely to be an internship with a family friend, while a poor kid will start out at minimum wage. THe rich student will visit top-tier post-secondary institutions to decide where to go after high school, while the poor student will choose between for-profit online schools, enlisting in the military, or starting a job that only requires a high school diploma. The poor people in america live in the most polluted neighborhoods that may not have access to fresh foods, making them more likely to get diseases related to diet and the environment.

There are a million barriers that poor people must fight through for survival, let alone advancement, that the rich and middle class simply do not face. These are "Structural Disadvantages" in our society.