 Third, the crux of the argument for the conclusion in step 4 is the idea that if everyone acts prudently at the decent minimum economic threshold of welfare to buy some kinds of health care, what they buy, assuming they bear the inclusive social cost of the insurance (including any losses of efficiency), will constitute the decent minimum of care. To say it is prudent for a person to buy the insurance (while bearing those costs) is (using the Ex Ante Pareto Principle) to say the person has better prospects with the insurance than without and that no one is worse off as a result. Presumably, however, this requires that there be a competitive market for such insurance (an assumption Dworkin had to make in his argument), and it is not obvious how to achieve that in light of the pervasive uncertainties that exist in medical markets (cf. Arrow 1963), a point Gibbard notes.