As an instrument for delivering publicity, terrorism clearly works. Or at least it did last week, when the hitherto obscure term “incel” went viral after Alek Minassian drove a truck into a crowd of pedestrians in downtown Toronto. Mr. Minassian, just before carrying out his attack, wrote a post on Facebook in which he proclaimed the arrival of an “incel rebellion.” Standing for “involuntarily celibate,” the term is used as a badge of honor among a fringe online subculture of misogynists who say they hate women for depriving them of sex. So now we know.

Were it not for that post, speculation about Mr. Minassian’s attack would have focused on its connection to the Islamic State. It certainly looked like an Islamic State attack: The terrorist group has been aggressively inciting its followers to kill Western civilians with motor vehicles, and since then there have been many such attacks. Mr. Minassian cannot have been oblivious to these horrific rampages and the tremendous publicity that they attracted. This was an Islamic State-inspired attack minus the Islamic State ideology.

Mr. Minassian is obviously a deeply troubled individual. And mass murder is driven by a variety of psychological factors. But much of Mr. Minassian’s trouble seems to have been fueled or exacerbated by the frustration and shame that accompanied his lack of sexual contact with women. This would have made him feel unfulfilled and indignant, and also weak and unmanly. The sense of shame from not being able to perform a culturally approved sex role may be a key to understanding his murderous rage. It may also be another thread connecting him to other violent actors whose ideology is different from his own, yet whose actions are similar. It is not difficult to spot parallels with the world of jihadism, where women and sex are similarly fixated on to an extraordinary degree.