But not everyone reacted to trauma by going into denial? Some people had really crappy things happen to them. They did not deny this, necessarily. They just found a way to move to the next things.
And note, that it wasn't everyone. Some people did not find a way to move on. Worse, some people likely perpetuated their trauma on to others.
"Denial" typically refers not to the denial that something bad happened to you, but to not see how you act it out on others (or yourself). It is exactly those in denial that would claim that they "have moved on", and try hard to make it look like they did also to those around them. It then shows up in violent tendencies, lashing out against kids, enemy images, patterns of avoidance, psychosomatic symptoms, burnout, addictions, obesity, sports injuries due to overdoing it, inability to sit still and listen, etc. - not necessarily PTSD symptoms.
And note, that it wasn't everyone. Some people did not find a way to move on. Worse, some people likely perpetuated their trauma on to others.