It hits different people in different ways, and often the strength of reaction can vary depending on your current mental state, particular specifics of the stimulus, how long ago the trauma occurred.
Specific trigger stimuli used to hit me a lot harder when I was younger, but I've had twenty-odd years to process things now. It still makes me feel deeply uncomfortable to have things close around my neck or face, or around large groups of aggressive guys.
I feel content warnings on difficult subjects can help. Most of the time, I'd be fine with reading about things that related to my particular traumas if I knew what I was getting myself in for - it's the times when it blindsides you and you don't have time to gird yourself mentally when it really kicks you. Also, some days if you're feeling fragile already, knowing to avoid it for today and maybe come back another day when you're feeling better able to handle it. For me at least, it's not so that I never suffer damage by being exposed to triggering things, but so that I can be on guard because I know it's there.
I think it definitely helps to think of post-traumatic stress as an injury - kind of like the mental equivalent of a broken limb. It can heal over time, but it may not set correctly and even if it does, there's still a structural weakness there. It does make you more susceptible to further damage.
The healing process can also be set back if you're continually knocking it against things, so it makes sense to guard it against damage. At the same time, though, putting it in an isolated bubble where it can't get damaged makes it incredibly difficult to use, too.
You need to find a risk balance that allows you to heal the injury, but also live your life. Having friends around who understand the injury is there and can avoid accidentally hurting you moves that balance further in the direction of living your life. But sometimes, you just need to armour up regardless of the restrictions it puts on you.