People in the second group have to work much harder than those in the first group to achieve well-being, even if they are professionally successful. People in the first group can afford to underachieve, since they will progressively become richer than those in the second group anyway.
The way I see it there is not simply a low and middle class, there is a multitude of subclasses among them that are mostly defined by inheritance. Partly as a result of it, we now live in awkward economic bubbles that don't mate with each other.