I saw a guy during the Leadville Silver Rush a few years back tightening a main pivot bolt on the side of the trail.
Ever since then, I’ve done a full bolt check before races, although have missed some. In JPs gravel pursuit a couple of years ago, the shifter dropped off my bars at about mile 100, and came about 1 inch from being chewed up in my front wheel. That’s now on my bolt check list. Like you say, the best lessons are the ones learned the hard way.