Final answer:
The phrase means that a wrong has not been properly corrected if the person seeking revenge is harmed in the process of enacting justice, suggesting successful vengeance must occur without negative consequences to the avenger.
Step-by-step explanation:
The phrase "A wrong is unredressed when retribution overtakes its redresser" means that a misdeed or injury is not properly corrected or made right if the individual seeking vengeance suffers consequences as a result of their attempt at retribution. Retribution must be carried out without negative repercussions to the redresser for it to be considered effective or successful. In essence, for justice to be served, the person inflicting the punishment must not become a victim in the process.