You encounter two inmates who are both combat veterans. One of the inmates has developed symptoms of PTSD, experiences such as flashbacks and nightmares, avoid conversation about his military experience, isolates himself from others, appears sad and irritable frequently, and has difficulty concentrating. The other inmate who had similar experiences in the military does not display these symptoms.

What explains the development of PTSD in one inmate and not the other? What research supports your reasoning?