Contrary to what many parents tell their children, talent and hard work are neither necessary nor sufficient for economic success. It helps to be talented and hard-working, of course, yet some people enjoy spectacular success despite having neither attribute. (Lip-synching members of boy bands? Money managers who bet clients’ retirement savings on subprime-mortgage-backed securities?) Far more numerous are talented people who work very hard, only to achieve modest earnings. There are hundreds of them for every skilled, perseverant person who strikes it rich — disparities that often stem from random events.
The role that this observation plays in the debate over how progressive the tax system should be was explained by Hal Varian:
In the simplest version of the Mirrlees model, taxpayers differ only in their ability: how much they can produce with a given amount of effort. One striking result of this model is that those at the very top of the income scale should face low marginal rates. This result emerges from a detailed mathematical analysis, but the intuition is not hard to explain. Let us assume, for the sake of argument, that Bill Gates made $1 billion in 2000, an amount larger than any other American taxpayer. Suppose further that despite the best efforts of his accountants, he ended up paying 40 cents of the last dollar he earned to the Internal Revenue Service. Consider the following thought experiment: drop the marginal tax rate from 40 percent to zero for all incomes above a billion dollars. The I.R.S. won't lose any revenue from this reduction, since no one has an income larger than $1 billion. And who knows -- the lower marginal rate might encourage Mr. Gates to work a little harder in 2001, producing new products that would make him, and the rest of us, better off. Of course, the fact that it pays to reduce the marginal tax rate for billionaires doesn't say much about what tax rates should be like for mere millionaires, a point that has been emphasized by Professor Mirrlees himself and confirmed by subsequent researchers, like Peter Diamond of the Massachusetts Institute of Technology and Emmanuel Saez of Harvard. But the intuitive argument presented above is pretty compelling: if income depends only on ability, those at the very top of the income-ability distribution should face low marginal tax rates. But perhaps this model is too simple. One might well argue that Mr. Gates, as productive as he is, doesn't owe his success entirely to ability: there was a lot of luck involved, too. And, if truth be told, that's probably true even for mere millionaires. So let's consider a different model: one in which differences in income are a result only of luck and have nothing to do with ability. In this case, the optimal income tax may well involve taxing billionaires at very high marginal rates. True, aspiring billionaires won't work quite as hard, since the after-tax reward from hitting $1 billion has been reduced. But the chances of becoming a billionaire are pretty low anyway, so taxing billionaires at a high rate won't really discourage much effort by those hoping to become one. Thus a model where luck is the driving force tends to yield a more progressive optimal tax than a model where ability is the driving force. This is about as far as theory can take us, but it highlights the critical question: How much income results from ability and how much from luck?