The core concept of capitalism is that capital works for you. It separates earning money from working. If you have enough starting capital, you don’t have to work at all, because you can hire people to work for you and you can even hire people to do the hiring for you. You can even abstract all that away by not hiring but instead investing, and you can even pay someone to do that for you.
If you have money in a capitalist society, you don’t need to work, and if you don’t have money, you can work all you want and you will still not become rich.
On the other hand, the American Dream says that if you just work hard enough, you will be successful, you will make it, you will become rich, no matter whether you have money and contacts or not.
These two ideas directly conflict each other.
That is only the case if the system is not capitalistic in nature, meaning that capital trumps work.
That’s the significant feature of capitalism over prior systems: Capital is more important than anything else.
Social mobility is a bug in capitalism, not a feature. Because if you have social mobility, then the rules aren’t loose enough so that capital trumps everything.
There’s a reason it’s called capitalism and not meritalism.
Luckily capitalism is not a binary thing and we don’t have pure capitalism.