I rode over a railroad track coming in to work today and suddenly heard a bad rubbing sound in the back of the bike. I stopped and looked. Tire and wheel were OK. Turns out my rear rack is rubbing on the top of the tire. The hardware is OK, so it must have been the weight of my stuff bouncing that bent the rack down toward the wheel. I bent it back to what I judged was an appropriate distance from the wheel and was on my way. No manuals, no tools, just simple roadside troubleshooting and a careful eye and hand to bend a part. I felt like there was a little bit of finesse involved in diagnosing the problem, judging where the bend happened, judging where to put my hands to bend it back and judging how far to bend it. An easy repair, for sure, but an example of pure skill that you're not going to learn from a book or YouTube video.