A 2015 review proposed three possible reasons someone might turn hikki. It could be that “overdependent” youths grew up in smothering families where they never gained autonomy or learned to trust people; “maladaptive interdependent” youths grew up in dysfunctional families, leading to bullying and unsatisfying relationships at school; and “counterdependent” youths are so burdened by high academic and career expectations that they withdraw.

The prevalence of hikikomori also speaks to the culture of mental health in Japan. A 2010 Journal of Nervous and Mental Disease paper proposed that hikikomori is used by laypeople to describe other mood disorders that they may not be familiar with, and that mental-health professionals may use it as a gentler way to talk about other issues, since clinical depression and its ilk are so highly loaded. The researchers reference a 2008 study of 97 clinical hikikomori patients which found that 26 percent had anxiety disorders, 8 percent had schizophrenia, and 23 percent had some sort of personality disorder — indicating that what manifests as hikikomori may be the result of one or more underlying, and possibly underdiagnosed, conditions. A 2011 pilot study found that similar sorts of social withdrawal exist around the world; surprisingly, some Japanese clinicians thought it didn’t demand intervention, while other countries recommended hospitalization.