"Truth is, all derailments happen SUDDENLY! "

Sometimes they do, and sometimes they don't. Seen my share of derailments too, from the nasty cars off in all directions kind to some that were more humorous than serious. Had one recently where a car 4 cars ahead of DPU power was off the rails. From the time I told the train to stop on the radio until it actually stopped, the car rerailed itself on a crossing and was sitting in the train like nothing had happened. Another time I was running a empty unit train around a sharp turn at a slow speed and felt a distinctive clunk on each of the six axles of the lead locomotive. I got the train stopped and sure enough there was a broken rail on the outside rail in the curve. I have no doubts that had I kept going some car was going to pick that break and send the train into the ditch.