All men (people) are created equal. That’s a central idea to America; yet, luck of birth has always played a role. Research now shows that being born poor limits the probability of upward mobility. Being born rich limits the probability of downward mobility. In America’s defense, there are no legal strictures enforcing class status, and there are always rags-to-riches and riches-to-rags stories; but there are sufficient social structures that discourage the poor and favor the rich.
(Click on the graph for the link.)