The reason is really quite easy, and simpler to demonstrate than often describe, why more rapid, more readily, and those with PTSD tend to get upset quicker than others at little dumb things.
I would like PTSD stressors represented to explain this, and you'll better understand the difference to those with PTSD, and those without.
Whether you realise it or not, everybody has this thing called "good stress" in their life, which consists of such things as getting out of bed, day to day endeavors, going to work, cooking dinner, etc etc. No problems with that one.
The apparent, when something bad happens, or is really hindering you, is normally classified as "bad stress", which PTSD stressors represented consists such matters as paying bills, cash, relationships, getting fired from your own job, etc etc etc. Everybody gets bad anxiety at some period within their day; it simply is dependent upon the sum, along with the individual themself.
Now, as you are able to view, Cup 2 represents a person that is normal, and with both bad and good stress. They still have plenty of room inside their cup without overflowing (exploding, fury, fury, etc etc). Before being pushed on the edge, a normal individual can take a lot of tension within their everyday life.
The issue with that is that we possess the same quantity of good and poor pressure as everyone else, though we also have this enormous ball of PTSD which features our traumas and more.
As you can see from this cup, with good pressure and PTSD, you actually don't have much room for anything else. A little "bad stress" to get a person with PTSD, and they overflow quite rapidly compared to anyone else.