Overprotected childhoods caused it.

National Review reports.

The Etiology of Trigger Warnings

Greg Lukianoff (president of the Foundation for Individual Rights in Education) and Jonathan Haidt (a social psychologist at NYU-Stern School of Business) have written the cover story in the September 2015 Atlantic, “The Coddling of the American Mind.” Their provocative article lays out the new college trend: excessive protection of students from having their feelings hurt. In other words, they analyze the brave new college world of lurking microaggressions (small but constant insults), incessant search for trigger warnings (warnings that help students avoid trauma), and prosecution of speech through campus codes and harassment charges.

Lukianoff and Haidt see the trend as student-led, often taking the shape of verbal attacks on faculty. They analyze the trend in the light of cognitive behavioral therapy, labeling many of the habits as if they were behavioral disorders.

For example, psychologists define “catastrophizing” as exaggerating or magnifying the harm of an event; Lukianoff and Haidt see trigger warnings as examples of “catastrophizing” an unpleasant event and trying to avoid it.