It's ingrained because we American's that support it keep seeing it through out our lives. My grandfather was a farmer born in the 1800's in southern europe, my father born in the1930's was meant to be a farmer as well. He disagreed with socialism's precepts as he believed the harder you work the more you deserve. So he left and bounced around other countries. Within 20 years of being here in the states he had paid off both a primary home and a summer home while the neighbor who had been here his entire life had a mortgage until the day he died. If you define "social mobility" as being too poor to afford food and then becoming ultra rich were you burn $100 bills to warm the room, then yeah its pretty damn rare. But if you see it as someone able to live the life they want, in the way they want to live it, then we have oodles of it. My dad was carpenter, we're not talking high end education, just the ability to look at a problem and find a solution that worked. Even though he knows jackall about computers the critical thinking skills he imparted to me about plumbing and electrical work were the foundation for everything I know today. My father is today at best right in the middle of middle class for a retired 80 something, maybe you consider that a failure of 'social mobility', he doesn't considering where he started.