Deep, dark and sometimes overwhelming, the human compulsion to seek revenge is a complex emotion that science has found incredibly hard to explain.

Despite popular consensus that “revenge is sweet,” years of experimental research have suggested otherwise, finding that revenge is seldom as satisfying as we anticipate and often leaves the avenger less happy in the long run.

Now, new research from Washington University in St. Louis is adding a twist to the science of revenge, showing that our love-hate relationship with this dark desire is indeed a mixed bag, making us feel both good and bad, for reasons we might not expect.

“We show that people express both positive and negative feelings about revenge, such that revenge isn’t bitter, nor sweet, but both,” said the study’s first author, Fade Eadeh, a doctoral student in psychological and brain sciences in Arts & Sciences. “We love revenge because we punish the offending party and dislike it because it reminds us of their original act.”

Forthcoming in the Journal of Experimental Social Psychology, the study provides a more nuanced understanding of both the benefits and drawbacks of revenge. Conducted with colleagues in the university’s Attitude and Social Cognition Laboratory, the study is co-authored by lab director and associate professor Alan Lambert and fellow graduate student Stephanie Peak.

Its findings are based on three experiments in which about 200 people in each experiment were asked to fill out online questionnaires rating the intensity of moods and emotions triggered by their reading of brief news accounts, including one that described the killing of Osama bin Laden by U.S. forces as a retaliation for the 9/11 terrorist attacks.

The experiments were designed to explore whether people are right in thinking that revenge has the potential to make them feel good, despite recent research that suggests otherwise.

“We wondered whether people’s intuitions about revenge are actually more accurate than originally anticipated,” Eadeh said. “Why is there such a common cultural expectation that revenge feels sweet and satisfying? If revenge makes us feel worse, why did we see so many people cheering in the streets of D.C. and New York after the announcement of bin Laden’s death?”

In experiment one, participants read either a “justice-is-served” news account of bin Laden’s killing or a nonpolitical control passage about the Olympic Games. They then rated how strongly their current feelings matched up with a random list of 25 adjectives, such as happy, edgy, satisfied, irritated, mad, upset or sad.

Although this framework is similar to one used in a 2014 revenge study by Lambert, researchers modified the data analysis phase to focus on measures of emotion, as opposed to mood. Lambert’s study and a 2008 revenge study led by the late Kevin Carlsmith at Colgate University both focused on mood and both found little evidence that revenge contributed positively toward it. Instead, people felt worse after taking revenge.

“In the case of the bin Laden assassination, this person is associated with an obviously horrific act — the 9/11 attacks, which provides reason why revenge may be an indirect source of negative feelings,” Eadeh said. “What our current research shows is that the way you measure feelings can be quite important.”

Psychologists sometimes use the terms emotion and mood interchangeably, but there are important differences, as evident in the current paper. Emotions usually relate back to some clear and specific trigger and can be intense but are often fleeting. Moods, on the other hand, may come about gradually, last for an extended time, and are often of low intensity.

In this study, Eadeh and colleagues used sophisticated linguistic tools along with a standard mood inventory to tease apart the differences in self-reported emotions after reading a revenge-related passage. This analysis replicated previous findings that showed reading about revenge put people in a worse mood, but it also found that the same experience was capable of generating positive feelings.

“Our paper consistently shows that the emotional consequences of revenge are a mixed bag, in that we feel both good and bad when we take revenge on another party. This counters some previous research on the topic, by our own lab and others, that revenge is a wholly negative experience,” Eadeh said.

To further test these findings, researchers repeated the experiment using different reading passages selected to avoid wording or content that might predispose readers toward a particular emotion or mood. To avoid stimulating patriotic emotions, for example, the Olympics control passage was swapped for a generic description of food allergies. The Osama bin Laden passage was altered to remove wording that explicitly described the killing as retaliation for the 9/11 attacks.

Despite these changes, the findings remained largely the same.

“We believe the reason people might feel good about revenge is because it allows us the opportunity to right a wrong and carry out the goal of punishing a bad guy,” Eadeh said. “In our study, we found that Americans often expressed a great deal of satisfaction from bin Laden’s death, presumably because we had ended the life of a person that was the mastermind behind a terror organization.”