The latch on the shop door taught me more than any class
Had a visitor at my forge outside Tucson about 2 months ago, older guy who does restoration work up in Flagstaff. He watched me struggle with an old door latch I'd been meaning to fix for weeks, just a simple spring pin that kept sticking. After I finally got it loose with a punch and hammer, he pointed at the worn spot and said 'you just made that part last 20 more years by fixing the strike plate instead of the spring.' Took me a minute to realize what he meant, the angle was off, not the pin. I spent the rest of the day looking at all my jigs and fixtures with fresh eyes, checking how parts actually meet instead of just swapping out the obvious broken piece. Anybody else had a moment like that where a stranger showed you something basic you'd been missing for years?
Man, that strike plate thing hits home. I do a lot of work on old bicycles and the same deal shows up with derailleur hangers, people keep swapping cables and springs when the hanger itself got bent two degrees in a crash ten years ago. The part that fails is rarely the part that's wrong, it's just the part that finally gave up. What gets me is how hard it is to see that on your own stuff, like your hands know the motion so well they stop asking why the motion was needed in the first place.