Engineers and the Jet
Back in the 60's, a jet manufacturer was trying to build a jet that would go mach 4 (4 times the speed of sound for you non-aeronautical types). Finally after many years of design, the jet was finished. A test pilot took it out for it's maiden flight. Everyone gathered around ... and the plane went to Mach1 ... Mach2 ... Mach3 ... Mach3.5 ... and the wings ripped off, the plan hit the ground and killed the test pilot.
The engineers went back to the design and spent months re-vamping it. They came out with the new and improved second version, but when they tested it, it had the same disastrous results: the plane's wings ripped off and the pilot was killed in the crash.
The engineers went through 7 iterations, until finally they were about to give up. They decided to contact Bob, a retired engineer with the reputation of being able to fix all problems.
Bob comes in, asks to see all the design figures, charts, and drawings, and takes them home to study them. He calls the next day and says he has discovered a solution to the problem: drill holes vertically through the wings at the exact spot where they attach to the body.
At first everyone argues - the wings are ripping off now, why drill holes to them? but Bob insists that it will work. So eventually, they give in and do it. The jet is tested later that day and not only does it reach Mach4, but it goes to Mach5.3 before the test is declared over and successful.
All the engineers rush to Bob and congratulate him for his uncanny ability to discover the solution. "How did you know?" asks one of the engineers.
"Well, I'll tell you. I was on the toilet, and it occurred to me - toilet paper never tears on the perforations."