I was on a walk about, in a sculpture garden in the middle of town. Old guy, big DSLR, looking professional. Three girls came up to me, 18 to 20 somethings, and asked if I could help. Their camera would not take a picture when they pressed the shutter button. T'was a Canon Rebel with a kit lens.
I used it, and sure enough, it wouldn't fire. Short version: it's would not fire because it would not auto focus and it would not auto focus because the lens was toast. Took me several minutes to figure that out, but when I finally tried to manual focus, the lens was stiff, irregular, and made a grinding noise. Then I noticed an abrasion on the front edge. It had been dropped on a hard surface. I cranked that lens back and forth several times, but no joy. It would not free up.
So I said, "bad news", and explained the problem. The girls' eyes glassed over. I had forgotten that young people don't want to understand a problem, they just want someone to make it go away. I handed the camera back to one of the girls and told her to look in the viewfinder and see that little flashing circle in the bottom right corner, which tell that it can't focus.
She held the camera at arms length to see the LCD. Obvious she did not know what a viewfinder was. Then I pointed to the focus ring and said, "turn that". She did, but I could tell it was her first time, so she had no idea what was normal.
So I put the camera in manual focus mode and told them they could keep shooting, but had to manual focus. They seem delighted. All they wanted was pictures and didn't care how they got them.