My 4-year-old son fell off his bike and scraped his knee while we were biking. It was very minor, with no blood or even redness. He seemed okay immediately after but then my wife wiped his scrape with some of her saliva and that set him off crying. He probably spent about 10 minutes crying about an action (the wiping) that took about 1 second. We tried but failed to console him until we finally distracted him with a mural.
Mostly, I was just thinking about how many adults do the same thing, including me. Something offensive happens and we keep thinking about it and letting it affect our lives. Why not just move on? Why live a bad moment more than once? Distract yourself with something better.