Montresor is a good example of why we should almost never take justice into our own hands. He believed he was justified in walling Fortunato up in a catacomb and leaving him in the cold and the dark to die. In his mind, this was just recompense for the thousand insults he had suffered from Fortunato.

Of course, we as readers are horrified by this sadistic act. It seems impossible that even 10,000 "insults" would justify treating Fortunato in that way.

This illustrates how easy it is to exaggerate what injustices have been done to us and, therefore, feel justified in taking disproportionally cruel revenge. For this reason, even though the justice system is flawed, it is better to put justice in the hands of dispassionate people who can objectively evaluate guilt, innocence, and a proper penalty for a crime. Too often, we can let our emotions get in the way.

That being said, there may, on very rare occasions, be a time when justice so terribly miscarries that we are justified in taking action. In Agatha Christie's Murder on the Orient Express, for example, a man who kidnapped and murdered a young child gets away with the crime. A group of people close to child decide to take justice into their own hands and together murder him on the train, each stabbing him once. Importantly, this group did consult with one another, and nobody acted as a rogue vigilante. Poirot, the detective who solves the case, does not turn these people over to the police. This seems to be one of the rare examples when taking justice into one's own hands was justified—though by a group, not an individual.