Recently I have been thinking in this vein too... This "American dream" is such a repeated cliché that some may think it's just that: a cliché in the minds of even Americans. But my current hypothesis is that many (most) Americans actually believe it. To the point of being blind of the actual nature of this "meritocracy".
This blindness to the fact that individual agency is not really as powerful as the "dream" states basically reinforces the idea that certain hard to change property of an individual (ie. Race? Gender identity? Sexuality?) must be the core reason for lack of success/progress: the biggot believes not all people are what it takes to succeed, and the biggot's prey believe their core nature/mark is the main reason why others don't support their progress.