As a leading researcher on suicide, Matthew K. Nock knows the subject’s grim statistics by heart. Suicide is the second-leading cause of death for Americans aged 10 to 34, trailing only accidents. It claims more lives around the world each year than war, genocide, homicide, and all other violence combined. And 50 percent of people who died by suicide saw a clinician in their final month, according to multiple studies in recent decades, including Nock’s own research.For Nock, that last statistic ...