Despite declining social mobility, mke_geek makes a fair point, being born poor isn't absolutely guaranteed to mean that you won't be able to have a meaningful or fullfilling life. I'm sure that many people who are born in remote villages with a subsistence lifestyle, that we would view as living in poverty, are happier than many people who are born in "first world" countries.

Anyway, OP is asking about choices, not situations that are inflicted upon them.

It takes work, and if people don't want to put in the work then they will never get there.

Socioeconomic mobility over a lifetime in the U.S. has always been dramatically overstated, but in the past 20 years its gradually gotten worse

"In the US only 32% of respondents agreed with the statement that forces beyond their personal control determine their success."

"According to a 2012 Pew Economic Mobility Project study[24] 43% of children born into the bottom quintile (bottom 20%) remain in that bottom quintile as adults. Similarly, 40% of children raised in the top quintile (top 20%) will remain there as adults. Looking at larger moves, only 4% of those raised in the bottom quintile moved up to the top quintile as adults. Around twice as many (8%) of children born into the top quintile fell to the bottom.[24] 37% of children born into the top quintile will fall below the middle. These findings have led researchers to conclude that "opportunity structures create and determine future generations' chances for success. Hence, our lot in life is at least partially determined by where we grow up, and this is partially determined by where our parents grew up, and so on." -Per Wikipedia

2012 was 12 years ago, mind you.

Also found this 2021 Guardian Article that claims

"What about rising from rags to riches? In the US, 8% of children raised in the bottom 20% of the income distribution are able to climb to the top 20% as adults, while the figure in Denmark is nearly double at 15%. Equality of opportunity is also much less viable in the US than in other OECD countries..."