The “American Dream” began as a promise of social mobility and meritocracy. The idea was that whereas in the rest of the world one’s social position was largely determined by the circumstances of one’s birth and little could be done to alter one’s status, America offered unlimited opportunity to invent one’s own destiny, limited only by one’s own skills, drive and character.
We still love a good story of how someone rose from inauspicious circumstances to prosperity because we really want to believe that we’re in control of our own destiny, and these stories seem to confirm that anything is possible. The dark side of this mythos is that it casts a shadow on anyone who seems to have “failed” by not rising above their circumstances; they must not have what it takes. And the flip side of that is that it can also cause those who have “made it” to fail to recognize how their success has been enabled by factors beyond their own merits.
This is all of a piece with America’s obsession with individualism. In a worldview where one sinks or swims by one’s own merits, everyone else is just so much stage dressing. That’s a shamefully self-absorbed “dream”.
While the details of what constitutes success does shift from generation to generation, It looks to me like that central premise—that anything is possible for the worthy—is still there. That’s not surprising, since this idea is a great driver of economic growth. A lot of effort goes into keeping this idea alive in the face of much evidence to the contrary.