He began his research with a simple question: Can chance alone account for wealth concentration?...He assumed that all entrepreneurs began with equal wealth. Returns varied, solely by chance...I'll spare you the calculus, but according to Fargione's model, by the "inexorable effect of chance," and chance alone, "a small proportion of entrepreneurs come to possess essentially all of the wealth...According to Fargione, greater variation in rates of return hastened the concentration of wealth.
That's not a model, that's an assumption. He assumed individual wealth varies randomly, and found the net inequality will be due to randomness. I understand that assumptions drive models, but the step between assumption and result has to be a little subtle or non-obvious. Here, he assumed everyone varied by randomness, and after doing this in Excel (really), it implied variation by chance is really random.
While it's important to remember that assumptions aren't models, they are perhaps more important, because as Darwin said,
False facts are highly injurious to the progress of science, for they often long endure; but false views, if supported by some evidence, do little harm, as every one takes a salutary pleasure in proving their falseness.
People who get excited about wealth being explained solely by effort or chance are making an important assumption about navigating one's life. Success is the result of randomness, effort, and ability. If you omit one of these, you will be miserable. A lot of growing up is about finding what you like that you are good at, and usually you like things you are relatively good at. Then practice that skill until you become excellent at it. The rest you can't really worry about even though that too is important, especially in explaining things like why certain people are really rich, which is often being in the right place at the right time. This should make us content because it's all we can control.
Anxiety should be not be ignored, but seen as what incents us to do our best--to observe the Serenity Prayer--because we worry all the time if we are doing our best given an uncertain future (in the end, it's the doers that prosper). For the existentialists Kierkegaard and Heidegger, this anxiety is the essence of consciousness (or sein), because we exist in time and are always thinking about an uncertain future in a way animals do not. They had very different solutions to this problem, and while I tend to find Heidegger's solution more fruitful, it clearly has more potential downside (Kierkegaard chose faith in God, Heidegger became an enthusiastic Nazi).
It's sad that some people see the disparities in income, and think this is all effort or all luck. In any case, this is a more damaging belief for their own self-actualization than any silly tax policy they envisage.