As a human, we are fragile. I am fragile. Unfortunately, those of us that have experienced more bad things than others, tend to be the more fragile party. Our experiences have made us stronger overall, but we all have our triggers...those triggers, no matter how hard we try, don't seem to go away completely.
Our triggers are all custom, you know..since none of us are exactly the same. While my triggers may relate to infidelity or not being enough (in relation to literally anything...suddenly being a perfectionist makes sense). Your triggers could lie with a place or action - something that even slightly reminds you of those bad things that have stuck with you all this time.