Not only "people are people", but there's a difference between what civilians and veterans may consider "less trauma than others". It's like going from comparing "apples to oranges", to comparing "apples to a Honda Civic".
Both environments are equally valid and relevant, as they both exist, but are different in scope. Vets are trained to compartmentalize the traumatic events they witness or experience. It's part of the training necessary to keep soldiers functional enough to continue fighting. Outside of hospital ERs, inpatient psych facilities, and war zones, most civilians don't usually have as much of a need to do so.
It can feel rather frustrating, even a bit humiliating, to have the years of experience to know you've overcome the impossible endless times, even when you had nothing but your wits and a need to survive... and one day, wake up and find yourself completely powerless against something inside your own head. Your frustration at having difficulty trying to understand what your Vet's dealing with, that's actually pretty common.
I'm surprised that more threads on that topic don't exist on here, but I'm sure that if you asked the admin they could offer guidance on how to start one correctly. The worst they can say is "no".
To put what
@joeylittle said in a simpler way, you can't rationalize irrational behavior. No matter what caused it, no matter when it happened, how severe or for how long,
PTSD is like living in an alternate universe where everything looks the same as before... but there's just something a little bit off and you can't quite figure out why.
A bit Heinlein-esque, but still a common frustration for both sides. After a while you just go with the flow, and take it one day at a time.