Among people I know who’ve had to defend themselves, PTSD is a great deal less prevalent in those who were successful. A person who is injured in a self-defense situation would have nightmares about it, while a person who succeeded in avoiding injury is not. The correlation is not perfect but very strong.
As with medical supplies or firefighting equipment, the training and the experience of the user is extremely important. But a physician without his tools is unlikely to be effective tending to a health emergency, same as a defender without her tools would be hard-pressed to manage a social emergency. In the end, the difference may be life and death (or a permanent disability), depending on the availability of both knowledge and equipment.