This is a write up of Glaucon's theory of justice as explained in plato's Republic II
Glaucon believes that justice is in reality a social contract we have created for ourselves to protect ourselves and to avoid the even greater harm, misery, and suffering that would come from not having it. For instance an extreme example would be, I would like to murder if I could get away with it, but I wouldn't want to be murdered myself. I fear being murdered more than I wish to murder others, so I do not do it. If I can cause suffering to someone they can cause the same suffering to me. Glaucon asserts that this is the only reason people follow laws and obey the rules of ones society(or someone else societal laws and rules if we are visiting a different country, city, society, etc.) because it is in our best interests. Glaucon brings up the story of The Ring of Gyges, a man finds a ring that turns him invisible, he can do whatever he wants with no consequence, so he sleeps with the kings wife and takes the kings throne for himself. He asserts that if such a ring existed that we would all be doing things such as murder, rape, theft because no negative consequences would follow from these actions.
Glaucon continues that if we were to give two men two rings that turn themselves invisible, both men would act in exactly the same way. If by chance one of them didn't do unjust things and chose to stay just, we would question why despite maybe praising them for it. Simply put if you had the ability to rob a bank for five million dollars with no consequences, not from the police, your friends wouldn't think any differently, people would think your still just as just as before, no possible repercussions then what reason would you have to not do it? I would think you’re crazy and find it odd that you didn’t but I may not say that out loud in fact I may praise you for it. But simply to keep up appearances and to dissuade you from causing me any injustices/suffering whether it be out of spit, profit, or having been convinced by me to do injustice and thus I am now suddenly your target.
Glaucon also touches on the topic of what it means to be a just and unjust person and what is the better of the two. Say a man who is unjust in the sense that he lies, cheats, steals and all the things we associate with an unjust man. but is praised as a good man, given rewards and beloved by people. And second we have a man who is by all accounts just and does just things but is thought to be a unjust man he is scorned and hated. That towards the end of their lives it would be argued that the unjust man who is honored and loved will have lived the happier more fulfilled life not the man who is just for its own sake but is hated by everyone and thought to be unjust. This would imply that it all comes down to how you are perceived, not the actual actions you perform.
Credit to Harvard.edu for supplying the photo