actually, not everybody gets PTSD in for example a combat situation, and Gabor Mate says that people who do develop PTSD are the people who have already suffered traumas as children; in a sense, childhood trauma is a preexisting condition.
A lot of PTSD is also not from combat all all- childhood emotional trauma alone can cause it. This is recognized now, but it took a while because initially it was discovered in war veterans and categorically excluded other groups- eventually they discovered that war wasn’t unique in causing the condition.
However, I would point out that Mates’ views are controversial, and don’t fully agree with other research on trauma and PTSD. He unrealistically associates essentially all mental illness and neurodivergence with childhood trauma, even in cases where good evidence contradicts that view. He claims ADHD is caused by childhood emotional trauma, although that is proven not to be the case, so I don’t put much stock in his scientific reasoning abilities- he has his hammer and sees everything as a nail.
