“Justice is doing one's own work and not meddling with what is not one's own.”Platon · Republica · -375 · 433a
Injustice is not wickedness but a role taken by detour: every part must stick to its own work.
For Plato, justice is not a list of rules but a state of order: each part of the soul and of the city does what fits it. The mechanism is the analogy between person and state — as the soul is just when reason rules, the city is just when each class performs its own task. Example: a state is corrupt not because people are wicked, but because judges play politics and politicians trade.
If justice is order, the key question is not "what laws exist" but "who has the authority to decide". Plato shifts the discussion from actions to roles: a decision can follow the letter of the law and still be unjust, if it comes from someone with no place to make it. Think of an apartment building: the owners' association president decides how shared money is spent, but cannot walk into your flat and rearrange your furniture as he sees fit. Same act, different role, different meaning. From here an awkward question arises: how do we recognize, in practice, who truly holds a role and who merely claims to?
Why it matters Useful when asking what justice means beyond laws: injustice often appears when someone holds a role and uses it for something else.