“Make sure the person whom you think wronged you is the person who wronged you,” says Charles L. Griswold, a philosophy professor at Boston University. Forgiveness means abandoning anger, and that can be long, hard work — possibly a lifetime’s worth. So before you embark, clearly identify perpetrator and transgression, and make sure the situation calls for forgiveness and not something else, like mercy.

Despite a seemingly endless supply of self-help and religious literature that urges bountiful forgiveness, be careful about offering it up willy-nilly. “Don’t act in a way that condones or enables further wrongdoing,” Griswold says. But take action. Studies find that anger, vengefulness and all the negative ruminations that come with not forgiving can damage the human organism, especially the heart. Indeed, so-called forgiveness interventions (essentially practice sessions) have successfully reduced symptoms in patients with coronary artery disease, chronic pain and even drug addiction.

Researchers disagree about exactly what constitutes forgiveness (though they concede that it involves “reducing unforgiveness”). While many theologians and philosophers think it can be unilateral, Griswold holds that forgiveness should be bilateral: For a victim to truly let go of his or her anger, the perpetrator must first admit responsibility. You can ask for an apology, he says, but you won’t always get one. Both parties should use direct and specific language. “Clarity is of the essence,” Griswold says. “If you fudge what it is that you’re doing, the process hasn’t been successfully completed.” And if the person who mistreated you is dead, has disappeared or is just an unrepentant jerk? “You have to find other ways to put aside your anger,” Griswold says.

Many religions teach forgiveness, but being devout is not required. Griswold has written about forgiveness in secular contexts because he believes that forgiving is one way our species can express true moral virtue. Humans hurt one another in tiny and immense ways, over and over, but we have also worked out this simple — yet sometimes profoundly difficult — act to free one another from some impact of that harm.