In case you think it was silly that you had to memorize those rules for your PPL: This morning when I taxied onto runway 10 at KCKF in Cordele, Georgia for takeoff, there was a balloon directly on runway heading. It was at about 500 AGL, less than a mile from the airfield, right in my upwind path. Wind direction was 45 to the runway but very gentle, so I held on the numbers for about 5 minutes while the balloon slowly drifted out of the way. When I took off, the balloon was landing in a field a few hundred yards to the side of the airfield. For a few seconds it looked like he was headed right towards me and intended to land on the runway. I started considering my options to get the heck out of the way. So no, it's not hypothetical. It can happen. Kicking myself that I did not think to take a photo.