Mending a bike puncture

Ellie's bike had a puncture today. I used some tyre-levers to prise the tyre off its wheel rim. Then I carefully pulled the inner tube out and was puzzled to see a large section had folded over on top of itself! How did that happen? A hurried previous repair? I attached a pump to the valve and pumped some air into the inner tube. Then I filled a bowl of water and plunged the inner tube into the water, shifting it along section by section. Suddenly a tell-tale stream of air bubbles revealed the source of an invisible hole in the inner tube. Right in the middle of an existing patch. More evidence of a hurried previous repair. I was struck by a few thoughts

The first is that air, like software, is invisible. To get the hole to reveal itself I switched to a different medium, from air to water.

The second is the importance of root cause analysis. Find the thorn and remove it. Otherwise you'll end up patching the patch just as I did.