One troubling aspect of the final police report on the October 1 Las Vegas mass killing is that no precise motive has been found for the killer, Stephen Paddock. The report, released on Friday by the Las Vegas Metropolitan Police Department, concludes:

Nothing was found to indicate motive on the part of Paddock.

The investigators’ interviews with Paddock’s brother Eric may reveal something:

Eric believed [Stephen] Paddock may have conducted the attack because he had done everything in the world he wanted to do and was bored with everything. If so, Paddock would have planned the attack to kill a large amount of people because he would want to be known as having the largest casualty count.

Paddock seems to have been disgruntled about life. Perhaps he carried a grudge against people in general.

A different story published in Gizmodo on July 26 suggests that it is not uncommon for people to hold a grudge and take revenge against strangers. An Alabama real estate agent, Monika Glennon, had been involved in an innocuous but heated online discussion with a stranger, Molly Rosenblum. The latter developed a grudge and, to exact vengeance, posted elaborate but totally fabricated allegations about Ms. Glennon on a website specialized in airing personal grudges—yes, such sites apparently exist. Gizmodo reports:

It was the online version of road rage; instead of pulling a gun on another driver, Rosenblum decided to drop a bomb on Glennon’s reputation.

The accuser claimed, with vivid details, that her husband and Ms. Glennon (who is also married) had had sex while visiting a house listed for sale by the latter. The post spread in cyberspace and became the top Google search result for Ms. Glennon’s name. All this caused her considerable trouble and distress. She had to spend $100,000 in legal fees to unmask her accuser and partly restore her reputation.

Psychologists have been interested in grudges and revenge (see for exemple Worthington and Sotoohi in the International Journal of Psychology Research, 2010). To my knowledge, economists have not.

We can certainly say that the cost of many forms of revenge has decreased in rich societies characterized by much individual autonomy—and dramatically so for ordinary people compared to higher-class individuals, who always had affordable revenge options. I suppose that ordinary people can also wreak vengeance in less advanced societies, for example by accusing somebody of witchcraft or of violating some tribal rule. In our societies, accusations of sexual harassment may be the equivalent. With the internet, anonymous revenge like Rosenblum’s have certainly become much less costly.

Other things being equal, when the price of exacting vengeance for a grudge decreases, there will be more demand for vengeance. Nursing grudges will also become more common since the benefit of forgiveness from the forgiver’s viewpoint (which includes the avoided cost of vengeance for him) is lower.

Other things being equal, when the price of exacting vengeance for a grudge decreases, there will be more demand for vengeance.

Another factor to consider is boredom. In a rich society, ordinary people have enough time to get bored. In a poor society, survival leaves little time for boredom. Both Paddock and Rosenblum (a poor single mother) may have been bored and disgruntled, although in different ways. Hobbies are a means to combat boredom, and their cost has also decreased, although obviously gambling did not work like this for Paddock. Culture—learned culture—can prevent boredom, but it has not necessarily increased in tandem with wealth.