An article on the website The Science of Us listed what they called "17 Things We Know About Forgiveness." Perhaps the most interesting scientific study on forgiveness noted who—or what—does not forgive. The article summarized the research this way:

Cats never forgive. Scientists have observed conciliatory behavior in many different animal species; the bulk of the research has been on primates like bonobos, mountain gorillas, and chimps, who often follow confrontations with friendly behavior like embracing or kissing. Scientists have observed similar behaviors in non-primates like goats and hyenas; the only species that has so far failed to show outward signs of reconciliation are domestic cats.

In other words, when it comes to forgiving others, don't act like a cat!