This is certainly true of Americans in "upper middle class" culture, but how true is it for the rest? I went to an average / below average American high school,

This is certainly true of Americans in "upper middle class" culture, but how true is it for the rest? I went to an average / below average American high school, and most of my high school peers are still living in my hometown. It's only a subset of the highly ambitious among us who left (some who entered spread out professions like health stayed; engineers left). And as an adult, many of my peers who grew up in economic centers like NYC and the SF Bay Area were able to stick around, regardless of profession.