system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How common are traumatic 'triggers' in the general population? Are they really dangerous?

I'd love to understand this subject better from a psychiatric perspective, especially with reference to any relevant literature.  

PLEASE: don't debate the merits of trigger warnings! Follow the subreddit rules!
gpt
basically a trigger can be anything that reminds you of some traumatic event. we'll ignore the entitled tossers who misapply the term to mean "things that make them a little upset" and stick to the actual psychology.

basically when you experience a really traumatic event it changes your brain, not in a permanent way per se there is therapy and such to change it back but the trauma is part of your memory and when the fear centre of your brain encounters that memory it freaks the fuck out and you are back in that life or death situation beating the shit outta a waitress who just dropped a tray behind you. 

reasonably though a trigger can be anything, a color, a song, a smell, a sudden noise and part of therapy is getting past this, usually through immersion therapy (introducing them to the trigger in a controlled environment so the brain stops associating that thing with imminent death or getting raped and starts associating it with nice things, so when it comes up your brain doesn't go straight to red alert.)