It's also possible to lift oneself out of low circumstances, but man-oh-man is it hard.
My father ran away from his home in the late 40s/early 50s as a teenager to escape crushing poverty in the midwest (where shoes were literally an item to be shared amongst his siblings and starting a full-time job at 13 was normal). He joined the army, fought in Korea, came home and became the first person ever on my father's side to earn a college degree with copious help from the G.I. Bill.
It meant he could move up to low-paid white collar jobs instead of blue collar labor jobs, but still he didn't become a "success." He taught school for a while, until the rampant crime of the poor parts of Chicago scared him away, and after that he bounced around in various jobs: owning a gas station, sales, traveling sales, etc. He finally settled in the business I grew up in. But it was not wildly profitable.
My mother grew up in a family of non-college educated sales people and housewives. She attended 1 semester of community college before dropping out, married my father not long after and only ever really worked in the family business. To my knowledge, only 2 people on her side ever graduated from college: 2 of her brothers, both became reasonably successful.
My parents paid the employees first before they got paid, so we often went months without money. I think during the best year ever, a year with near monthly lucky breaks, my parents combined income may have broken $90k. During our worst year, we spent 4 months homeless, living in a roadside motel full of drug addicts and other questionable types. When we had a home
College and school was not a priority for me, I never took the SATs, and I guess it was assumed I would just inherit the family business. There's a long(er) story in between, but I'm the first person in my family to earn a Masters Degree and feel like I'm reasonably successful, upper-middle middle-class. I didn't do it all on my own, I was given some great opportunities and help along the way and seized those moments like my life depended on it and worked my tail off.
A great many of my peers fell into two camps, those born into wealth pretty much all turned out great, great educations, great careers. I'd say I'm about middle of the pack with these folks. A few slid down a bit, usually various substance abuse issues were involved. But even then, many of those folks had the family resources at hand to turn their lives around when they had solved the substance problems.
Those born into similar economic situations that I grew up in tended to stay in those situations. If they grew up in a single parent family and their mother worked part-time at the local Circle-K, there's a big chance that that's where they ended up as well or fell down even further. Thinking back, I can only think of 1 or 2 other kids I grew up with who worked their way out of the socio-economic conditions we grew up in. By and large, most of them didn't find a way out.
What's disturbed me are the people who were also given great opportunities but squandered them. The ones who somehow were sponsored to attend college for free, but failed out because of too much World of Warcraft, or couldn't figure out how to operate a condom and ended up with 3 kids they couldn't care for. Pondering these folks, I suspect that the "Marshmallow Effect" is a real problem for them. Most of the life choices where they lost an opportunity to get ahead involved them taking a strategic and difficult, long, view of their life...with the option of doing something that felt good at the moment instead. They usually took the feel good option instead.
Case-in-point, my best friend of more than 20 years has had opportunity upon opportunity come his way and blow them and has been more or less perpetually bankrupt since we got out of High School. He recently ran into yet another serious money and family problem prompting us to have a serious grownup conversation about his life-choices to date. He wasn't even aware that he had had these opportunities I spoke of and our parting words were that he was going to make a concerted effort to get a better job and work on solving his money situation instead of leeching off of everybody around him.
It's 3 months later, he hasn't finished his resume, has "applied" for 3 jobs in that time, and moved to a more expensive apartment he can't possibly pay for given his current situation. Why did he move? "My lease was up and I wanted a better location, near a better school district for my son." His son who won't start school for 3 more years. With so much left to do, you'd expect that he be spending his nights and weekends working a second job, or some other meaningful activity. No, Steam shows he spends most of his time after work screwing around.
This is all anecdotes of course, but I suspect that it's applicable in a great many places as well. Help and opportunities are out there if you're poor. But you have to work 2 or 3 times as hard as the other person who grew up rich and wealthy. While my school-mates were being given a generous monthly allowance, their parents credit cards, new computers and condos closer to school with a brand new SUV to drive the quarter mile there and back, I was working a full-time job, taking night school, driving an hour and a half to school and back in a car I was praying wouldn't die on me, sleeping 4 hours a night, and literally eating instant noodles 3 times a day for months on end. But I'm thankful every single day that I had: a car to drive, a job to drive to, school grants to cover my education, teachers who understood my situation and let me turn things in a day late, a boss who understood as well and let me take time off for exams and studying and more. I treated each of those opportunities as precious and tried to make 130% of them. And as time went on, doing so turned each of those initial opportunities into more opportunities, a snowball effect.