When the maintenance men finally saw the light.
In the 1980's, there was a great deal of concern about the erosion of the Lincoln Memorial.
The maintenance staff were asked what they thought was the cause.
They responded that the damage was due to a strong cleaning spray used to keep the masonry free of bird poo.
So they installed bird nets.
However, this was an unsightly solution that many tourists complained about.
So they removed the bird nets.
They then thought about what was attracting all the birds to the memorial.
It turned out to be spiders.
After dark, the spiders would climb the memorial to eat the midges that had migrated from the nearby marshland.
The committee considered using insecticides but they posed an obvious health risk.
Finally, someone had the smarts to ask ‘why were there so many midges on the memorial in the first place?’.
The answer: because it was floodlit.
They consulted the entomologist Donald Messersmith who advised them to turn the lights on later in the evening and switch them off earlier in the morning.
An 85% reduction in the number of midges.
Fewer midges meant fewer spiders which, in turn, meant fewer birds and this resulted in less bird poo.
This is a classic example of root cause analysis. The solution in this case is not about answering a masonry cleaning problem but is, in fact, a seemingly completely unrelated issue of insects and their behaviour.
To get to the root cause of a problem you need to keep asking questions.
The 'Five Whys' exercise is designed to do just that.