Rawls' 'veil of ignorance' is the most powerful tool for thinking about fairness

In A Theory of Justice (1971), John Rawls proposed a thought experiment: imagine you must design the rules of a society without knowing what position you would occupy in it — your race, gender, income level, or natural abilities are all unknown. Behind this 'veil of ignorance', what principles would you choose? Rawls argued you would opt for equal basic liberties, and then for economic inequalities only insofar as they benefit the least advantaged group. The device became the dominant framework in political philosophy for evaluating the justice of institutions.

Source: Rawls, A Theory of Justice (1971)