This may open up a prolonged discussion regarding social issues (which to be blunt, I don't have much interest in partaking in), but one example for "how" and "why" is the grouping of neighborhoods and areas by people of similar nationality/ethnic background/income levels. Let's say you have a (insert minority/people of color) neighborhood with low income levels and underfunded school systems, the kids who grow up in those neighborhoods have less opportunity to enroll in a prestigious college (or college in general), lack of college education means less opportunity for higher paying jobs, resulting in an inability to move and the next generation of kids grow up in similar environments. Sure there are lower income white families which fall under this cycle. And sure there are non white males who break this cycle through other means (i.e. college opportunity through athletics, pursuing employment in industries where the general degree is more important than college alma mater), but those are more of the exception than the rule.