This means that we put aside such factors as race, gender, and social class and concentrate on which kind of society would best maximize liberty. It also means that we don't concern ourselves with what's best for us, but for society as a whole.

Rawls believes that by doing this we will arrive at the kind of liberal state and society that he strongly endorses. If we operate behind a veil of ignorance when determining the allocation of resources in society, then we'll inevitably choose a system which would be as just and fair as possible. Because we're behind a veil of ignorance, we don't know where we'd be in this hypothetical society; we could be fantastically rich or dirt poor; we could be a member of the dominant class or part of the exploited class; we could be racially privileged or subject to bigotry and repression. We just don't know. So it's better to be on the safe side and devise a system based on maximizing equality, fairness, and justice. 

For Rawls, "the veil of ignorance" is the manner by which decisions about resource allocation and political execution should be made.  It is a tool to ensure that justice involves a sense of fairness.  The veil itself is a concealment tool that prevents individuals from fully understanding where they would fall in a social setting.  The term "ignorant" might be too harsh.  Individuals are not fully clear on where they would fall because the veil precludes them from absolutely knowing their placement.  In this light, individuals would choose to protect those on the lowest rung because that could be where they would fall.  It is because of this that the veil of ignorance allows for a more pure sense of decision making because it is the mechanism that allows for individual and collective interests to converge.

In John Rawls's hypothetical model of how to build a just society in his book A Theory of Justice, the veil of ignorance is a key component. The veil of ignorance means that before the theoretical new society is constructed, none of the participants will have any idea of what their status in that society will be. The veil of ignorance assures that nobody knows in advance if they will be rich or poor, from a high-status or low-status group, talented or handicapped, or even what their psychological mindset will be. Every person has to assume, therefore, that they possibly could end up on the lowest rung of society without any special attributes or the psychological makeup to have an edge over others.

The veil of ignorance is crucial to the building of a just society. When people don't know where they will end up, Rawls argues, they will place a very high value on constructing a society that is just by being fair to all its members. By doing this thought experiment, Rawls tries to show that it is not aggregate or average happiness that is most important to social well-being, but the assurance that everyone will be dealt with fairly.

The veil of ignorance is a very important part of Rawls’ argument in A Theory of Justice.  It allows us to evaluate possible actions without prejudice.  This makes it possible for us to do a better job of understanding whether a potential action would be just.

Rawls says that we must use the veil of ignorance when trying to decide if a certain way of ordering society or changes to our society are just.  To use the veil of ignorance, a person must think about society without knowing what place they hold in that society.  For example, if we are going to introduce more free market reforms to ensure that people have to compete to prosper in our society, we have to think about this without knowing whether we are likely to be well-placed in that competition.  It is easy to advocate for more competition if you have been born to a middle class, educated family.  But what if you do not know whether you are going to be placed in a lower class family where no one is educated and you have no way to compete effectively?  Your perspective on the justice of this course of action might be different.

This is what the veil of ignorance does for us.  It allows us to think about changes to our society in a more objective way. If we effectively use the veil of ignorance, we think about how changes will affect everyone in our society, not just those who are like us.

Rawls's veil of ignorance removes the element of self-interest, which is an omnipresent factor in political thinking, to show that fair and just distribution can be defended on rational grounds if one considers the whole of society rather than a single faction within it.

Behind the veil of ignorance, one has no idea what position one will occupy in society. This solves the problem of partisanship. In political arguments, wealthy people often argue for unrestrained capitalism or even for forms of government which benefit the rich even more obviously. The working class might argue for strong unionization, and the poor and destitute, or those who advocate for them, will favor comprehensive social programs that provide housing and food.

Behind the veil of ignorance, the person making the decisions does not know whether they will be rich, working class, destitute, or occupying some other position in the society in question. It therefore becomes rational, even from the perspective of self-interest, to design a society that is as fair as possible, so that people in all positions are treated justly and no one is placed in a disastrous situation.

The veil of ignorance, therefore, neutralizes the effects of self-interest by ensuring that the subject's personal interests are unknown. While self-interest may be rational on an individual basis, Rawls argues that it is irrational to take it into account when making decisions which affect everyone in society.