For some people it is...
After serving for 6 years, with two combat tours in Iraq, I spent nearly 5 years working in the research department at the VA Hospital in San Diego. I worked on PTSD research with active duty Marines from the nearby Camp Pendleton EOD unit and with veterans from all branches.
Some of our subjects were diagnosed with PTSD and their symptoms got better over time with treatment. Some refused treatments and their PTSD got better on its own. Some subjects had debilitating PTSD symptoms for years and they never went away, even with treatment.
The sad truth is that we still don't know what causes PTSD, and we don't know how to effectively treat it in all cases. Some people do better with meds. Some do better with group therapy. Some do better with individual Cognitive Behavioral Therapy.
I also saw correlation between long term PTSD and a limb lost during the traumatic event. And this often led to other issues like phantom limb pain, depression, etc.
It's crazy how far medicine has come in the last 50 years and we still can't fix everybody.
So, in conclusion, PTSD is not the same for everyone. Some people get over it quickly. Some people carry symptoms forever.