I don't think they mean literally traumatic, but more like a bad breakup, or falling out of a tree. You survive -- maybe barely -- but its no more traumatic than a scrape or a bump. I still remember the first "major" injury I have (from jumping off a the top of a car at 4 years old). Not like it was yesterday -- no PTSD there -- but it was the first time I scraped my knee. I'll probably never jump off a car again.