Sometimes rich people do come from poverty. Sometimes middle class people come from poverty and rich people come from the middle class. And sometimes rich heirs and heiresses go bankrupt and fade into obscurity. Why does this happen? Because the people who improve their position are either intelligent or diligent and the people who decline in position are either stupid or lazy.

To whatever degree these traits are genetic, you’d expect them to get roughly sorted out to the point where social mobility would decline, but it wouldn’t disappear entirely.

> Because the people who improve their position are either intelligent or diligent

Or corrupt, or given a leg up through connections of ones father or school.

> and the people who decline in position are either stupid or lazy.

Or unlucky. Or got ill.

Your ideas sound very Victorian to me. I have noticed that most people who did get rich assume it is something special about themselves that did it, I'm guessing you are one of them.

Jokes on you, I’m not even rich.

I’m talking about broad population-level averages. Maybe you define “luck” as an actual quantifiable trait that measures whether or not you’re blessed by God, but I define luck as a completely random variable that produces noise in the individual case but does not affect population-wide averages.