Why do some victims of violence develop mental illness?

Why do some victims of violence develop mental illness?
Events that lead to actual loss of life or events that were life-threatening are more likely to lead to
PTSD. Man-made disasters such as terrorist violence may be more traumatic than natural
disasters because they can seem so senseless. Survivors of traumatic events in which others died
may also feel guilty or blame themselves for not having done enough to save the others. The
greater the loss of social support and community bonds (as can happen in war), the greater is the
risk of PTSD.