On an otherwise ordinary Thursday, a 14-year-old entered a middle school in the southern city of Kahramanmaras, opening fire on two classrooms, killing eight students and a teacher . The shocking attack followed another school shooting two days earlier in Siverek in Turkey’s Sanliurfa province, in which the gunman wounded 16 people before killing himself in a showdown with police.  While it often seems that such attacks come out of the blue, they are rarely spontaneous. Instead, mass shootings generally follow a narrative that regularly includes escalating grievances and missed opportunities to intervene. What do we get wrong about mass shooters? A shocking act of violence like the one in Turkey can appear to come out of nowhere. But experts say that impression is misleading. John Horgan, who directs the Violent Extremism Research Group at Georgia State University in the US, says the idea that attackers simply "snap" is one of the most persistent myths.…