[vannevar]

You are making the common mistake of confusing two different things: the absolute capacity for an individual to improve their income over their lifetime, and the relative capacity to improve based on their current decile. If progress depended solely on merit, you would expect economic growth to be more or less evenly distributed across the percentiles---the "rising tide raises all boats" idea. That this doesn't happen suggests that people in higher deciles not only have more wealth, but are more likely to acquire additional wealth. Many wealthy people---and even some poorer ones---maintain that this is because the wealthy must be more industrious. But the vast majority of wealthy people started life in the upper deciles. And it's clear that having wealth makes it easier to make more wealth.

If you doubt this, consider the following thought experiment: imagine two strangers, identical in ability. One wins a million dollars in the lottery, the other is poor. If you were forced to wager your net worth on which twin is likely to make the most money over the next 12 months, who would you bet on? Now think about what kind of qualities would it take to get you to change your bet. How much smarter and harder working would the man with nothing have to be to overcome the advantage of a million dollars? Or even $100,000? You might say, yes, maybe in one year money would have the advantage---but surely an advantage in industriousness would win out in the long run? The mathematical answer is no, because the lottery winner will have a bigger advantage at the beginning of year 2 than he did at the start. If you bet on him in year 1, the bet is even surer in year 2. The reality is that he will continue to pull away. And that's what we see in the real world distribution of wealth: the gap between the wealthiest decile and the next poorest continues to expand, creating increasing social and political strain, as we can plainly see today.