A deep down terror that they too could be poor, not that they would say that. Poor people get "othered," their poverty explained away as "part of their culture," a culture which is "naturally" "wrong" and the cause of their poverty. If only they'd behave "properly" they wouldn't be poor anymore. That last sentiment can be expressed in many ways but it's always the same at heart.
Since I'm in a disclosing mood today I'm going to disclose a some more. I was born into a very wealthy family, not that I was aware of that since it was in all ways dysfunctional, but still I was born into that culture (social class is very much a culture as much as moving from one country to another, sometimes more). I am also disowned by that side of the family and a bit cool with the "done good since WWII*" side of family and have been for a very long time. (*That side likes to call themselves "working class" but they're so not, they've never been culturally working class, they were landowners who got poor for two generations and made it a mission to make it back where they belonged.) Often I have gotten a boost up by my inherited demeanor (that's a privilege it took me a long time to understand I have), but it's poor people who saved my bacon. I had nothing much of any use, was underage, and not even out of school yet. It was a working class foreman who gave me an actual job, it was poor people, cleaners, cashiers, janitors who taught me how to be poor and if they had not I would not have survived. Everything I knew about budgeting and money and "how stuff works" didn't fit my new circumstances, it was like being in another country. As a bit of an aside, it's the transition between poor and middle class that's tricky because strategies that are crucial when you're poor will harm you a few rungs up and vice versa. Deciding when to change tack between systems is hard and there will be mistakes along the way that can keep a person bobbing between the two getting the worst of both worlds. Not enough people understand that.
Yes, the upper class are more honest but that's because they can afford not to be anxious.