James Kwak and Richard Posner argue that it's all due to luck:
Luck, Wealth, and Richard Posner, by James Kwak: I disagree with Richard Posner ... on so many things that I always worry when he seems to agree with me. Did I write something stupid? I wonder.
A friend forwarded me Posner’s latest blog post, “Luck, Wealth, and Implications for Policy,” parts of which sound vaguely like a post I wrote three years ago, “Do Smart, Hard-Working People Deserve To Make More Money?“ ... In that post, I argued that even if differences in incomes are due to things that people ordinarily think of as “merit,” like intelligence and hard work, that doesn’t mean that rich people have a moral entitlement to their wealth, because they didn’t do anything to deserve their intelligence or their propensity to work hard. In summary, “I have little patience for the idea that rich people deserve what they have because they worked for it. It’s just a question of how far back you are willing to acknowledge that chance enters the equation.”
Posner now goes even further than I did: “I think that ultimately everything is attributable to luck, good or bad,” he writes, including the propensity for working hard, a low discount rate, and so on. “In short, I do not believe in free will. I think that everything that a person does is caused by something. . . . If this is right, a brilliant wealthy person like Bill Gates is not ‘entitled’ to his wealth in some moral, Ayn Randian sense.”
He goes on—he is still Richard Posner, after all—to argue that tax policy should be concerned solely with incentive effects. ...