/lit/ - Literature

>>13592939
It's actually a central thought of Plato's ethics. When you read the Republic, you will find its deeper meaning.

According to Plato, a "just mind" (ψυχη is normally translated with "soul" instead of "mind", but that's misleading since the term "soul" seems to mean something else nowadays) is a mind which is "in good order" and in "harmony". And only a man with a mind which is in good order can be a happy man.

What does "in good order" and "in harmony" mean?
There are three parts of the mind: the reasonable part, the fortified one (the will) and the compulsive one (the desires). Those three parts have to be established in a certain hierarchy if your mind is supposed to be well-ordered, which is as follows:
The reasonable part of the mind is the only part which can recognize the "idea of justice" (which is the idea of the whole system I'm describing here). If it recognizes said idea, it knows what justice is and is therefore "wise" and "considerate" ("considerate" means: it's acting in accordance with the idea of justice). Neither the will nor the desires are able to recognize the idea of justice since they're not reasonable.
According to the idea of justice, the reasonable part convinces the will to act (want stuff) according to it. Since the will is unable to recognize the idea of justice, it has to believe in it. If the will deeply believes in the idea of justice and follows it against all attacks, it becomes "brave" and "considerate".
Those attacks are coming from the desires which drive to everything feasible including acts which aren't in accordance with the idea of justice. Therefore, the brave will has to suppress all desires which don't aim at considerate acts. Thereby, the desires become considerate and the idea of justice is put fully into effect. The just mind, the well-ordered mind, the harmonic mind is actualized.

Since Plato identifies happiness (ευδαιμονια) with said harmony of the mind, it becomes pretty evident why he thinks someone who's inflicting injustice is more miserable than someone who suffers it. Someone who's inflicting injustice is simply far away from an well-ordered mind and is therefore really, really unhappy.

Funnily enough, Kant pretty much says the same (which would be a little bit much to put down here) - the main difference between Plato's and Kant's ethics is that Kant doesn't identify the good (autonomous) will (which acts according to reason instead of desire) with happiness and therefore as an end in itself. Instead, he sees it as a means to an end which is eternal happiness in paradise. Therefore, Kant thinks, the "moral law in our hearts" is an indication (if not a proof) of the existance of God since it would be useless as long as there's no otherworldly reward for obeying it.