1).Well there are many reasons on that it could be a car accident or A death of a parent or sibling But What I would say IS a Death from your family if you see it your else fin front of your eyes it will scare it will scar badly at around 13 to 15 Because The Teens are learning new things and seeing death while change can scare them.
2).Damaging your self can also scare you like when your older and you smoke and It really Damages you and your health that can also influence a person on scaring them maybe every time they go somewhere or look down on what they did to them self's could be Good or Bad.