A commonplace example of economic mobility: most of the sons and daughters of professors at low-prestige colleges have no problem earning two or even three times what their parents earn, if money is what they decide to pursue. They have all the tools required to enter a profession such as engineering, medicine, or law. If you have the cultural and intellectual prerequisites to be financially successful in America, an initial lack of money won't stop you from becoming a prosperous upper-middle-class professional.
The barriers between the lower class and the middle class (including its upper reaches, the professional class) are cultural, not economic. Even people who seem to be held back by economic barriers are held back because of cultural barriers -- they don't know how to play the game and inspire the trust (both personal trust and the kind of impersonal trust embodied in a good academic, criminal, and credit record) that allows them to overcome the economic barriers.
The barriers are easiest to see in extreme cases. For example, inner city adults who can't keep the jobs they're placed in because being ordered around fills them with rage, or because they don't realize they can't disappear for a week without telling anyone, even if they were dealing with their father's death and funeral in another state. Or poor kids who don't know there are lots of federal student loan programs with favorable terms. I know savvy kids who took loans they didn't need because the terms were ludicrously favorable, but some kids drop out of school and take menial jobs because they don't know that debt is a normal, accepted way of paying for college.
The extreme cases are easier to see, but there are milder cultural challenges that are much more pervasive. Having worked for bosses from other cultures, I know that the consequences for being late with work depend greatly on how the situation is framed, and the "right" way to say "I worked my butt off on this, but it's harder than I thought" or "I've barely worked on this because you've had me putting out fires for the last two weeks" is dependent on culture. Even something as simple as acknowledging criticism is culturally sensitive. If your boss thinks you are blowing off criticism or being disrespectful, it can be a huge disaster. Understanding the differences isn't always enough. I quit working for one guy because I just couldn't adjust to him. (It may have been cultural, or just personal.) He was very emotional and assumed a close personal relationship with me. I like to play things cool and assumed that our friendship outside of work and our working relationship were separate. If I played it cool and didn't get emotional when he did, he thought I was blowing him off or showing indifference to him and our work. I was extremely stressed out by his displays of emotion at work. I found it extremely draining to try to respond with the appropriate emotions when all I really felt was distress and resentment that he was polluting (as I saw it) our working relationship with his unfiltered emotions. My only idea of how to display unpleasant emotions in the workplace was to mute them and deal with them by dispassionately discussing the concrete issues from which they stemmed. I was utterly miserable until I quit -- probably he was, too. And this was between two people with similar liberal political and moral convictions who were both educated in American universities.
I think one of the biggest cultural questions that causes problems between people is what it means to have authority to give someone else orders. To me, the power to give orders is inherent in roles. If someone is my boss, they can tell me what to do. They might give me latitude, and I might try to persuade them to give me different orders, but if they give me orders, that's fine, I do what I'm told. It doesn't mean they're higher or better than me. It doesn't mean they're smarter or stronger. It's just a matter of the roles we play in the business (or sports team or what-not.) In some cultures, authority means personal superiority. Naturally, these different interpretations create anger, insult, and resentment when they come together.
The Republicans played on this expertly when they described Sonia Sotomayor as "bossy." It won't sink her nomination, but it evoked a stereotype that has very intense emotional connections. It worked perfectly on me. I grew up in a place with a sizable Hispanic population. In Hispanic culture, authority tends to mean superiority. (One book I read said that in Europe, cultures believe in authority in rough proportion to how strongly they were influenced by the Roman Empire.) Of course, teachers have authority over students. When my Hispanic teachers talked to me, they talked down -- down from their superior intelligence, wisdom, education... all assumed to be superior because they had authority over me. My non-Hispanic teachers largely did not talk to me that way -- their default assumption was that we were equals who happened to be playing roles (teacher and student) in which they had the authority to boss me around and grade my performance. (Of course, there were exceptions on both sides.) The anger I felt at the way my Hispanic teachers treated me... well, I can still feel it today. To my mind, they had no good reason to assume they were better than me, and their assumption interfered with my education because they maintained their pretense of superiority at the expense of their academic objectivity. To their minds, they had to maintain a pretense of personal superiority, because otherwise they would lose their authority to give orders and maintain order in the classroom. So they talked down to me, patronized me, and made a point of responding to any show of knowledge or intelligence on my part by bossing me around even more. Now I'm probably rambling because the anger is running away with me.... But you can imagine that a Hispanic kid dealing with non-Hispanic authority figures might misread their attitude and think they are weak and should be disregarded.
Anyway, I'm sure many white Americans have the same kind of painful culture-clash memories of Hispanic authority figures as I do, so describing Sonia Sotomayor as "bossy" and "overbearing" is a clever way of turning her, in my and other people's heads, into an authoritarian, patronizing Hispanic stereotype. Which, if true, would be a great reason for excluding her from the court, since the political ideals of the United States are (all my liberal tolerance aside) incompatible with belief in the natural superiority of those in power. But there's no reason to believe she is anything like that stereotype, and there are excellent reasons to believe otherwise. She was successful at Princeton and successful in the U.S. legal system. Along the way, she worked productively with, and earned the respect of, lots of people to whom authoritarianism is anathema. I'm sure that given what she has accomplished, she must be conscious of the issue, must understand it thoroughly, and probably comes down on the same side of it as most other Americans. But the stereotype retains its emotional power. Even after thinking through the issue and rationally reassuring myself, the stereotype still holds sway over my emotions. (Damn those culturally savvy Republican attack dogs! They've taken over a little part of my brain :-( )