"Difference between night and day": Adventures in root-cause analysis

Last week we talked about a specific problem-solving discipline. Here's another case of problem-solving, involving an elegant example of root-cause analysis. 

A while ago I stumbled across a video that gives a perfect example of good, pragmatic root-cause analysis. The National Parks Service found that the stone of the Jefferson Memorial in Washington, D.C., was deteriorating. The analysis of what was causing the problem turned out to be a classic example of 5-Why methodology. The video is less than two minutes long:

Note that this is a perfect example of how 5-Why is supposed to work: you keep asking "Why?" until you get to a point where you can find a pragmatic solution ... and where you can't go any farther without giving up on pragmatism altogether.

• Trying to stop the birds without stopping the spiders would have been hopeless.
• Trying to stop the spiders without stopping the midges would have been hopeless.
• On the other hand, nobody asked "Why do midges come out at dusk?" That's just a fact, and there's nothing we can do about it. (I've said before that if you start asking "Why?" about fundamental facts of nature, you've gone too far. Real root causes must be actionable.)

In that whole chain of causality, there was one sweet spot, flanked by impossibilities on both sides. That's where the solution lay.  

Not all root-cause analyses are this elegant, but this is certainly the goal to aspire to.