What kind of world would we want to live in if we couldn’t know for sure our place in it ahead of time? Presumably, we would not want a world where we might be born in the wrong place, the wrong nationality or the wrong sex. We would probably define as a just world one that we would not regret being born into. John Rawls suggested this approach.
We can take this in three directions: 1. We can use it to design a model world that we would not mind being born into wherever. Odds being what you would feel comfortable in terms of number of chambers loaded before pressing trigger. 2. We can use this standard to judge the actual world we live in. 3. We can talk about why a person or people in general would be satisfied (or not) with their actual place in the actual world. Here we can also talk about why reason – and the need for others – should take us into a concern with justice for others even if pleased with our own situation. This last seems a call to action.