Problem: The Washington Monument is deteriorating

        Why? Harsh chemicals are being used to clean the monument

        Why? The monument is covered in pigeon droppings

        Why? Pigeons are attracted by the large number of spiders at the monument

        Why? Spiders are attracted by the large number of midges at the monument

        Why? Midges are attracted by the fact that the monument is first to be lit at night.

    Solution: Turn on the lights one hour later.

This is a massive over simplification of the 5 whys process. The author seems to be implying that this is the core of the process when it is not, it is merely a simplified example what the process would look like to someone unfamiliar with it.

Without getting into a massive amount of details the following things are important to note about 5 whys in lean.

5 whys isn't meant to arrive a a single conclusion or solution, it is meant to provide deeper analysis so that an appropriate and proportional set of countermeasures can be proposed and considered. The key concepts being a "set" of countermeasures and "considered".

5 whys does not need to exist in a vacuum as a problem solving tool. It is often just one such tool in a more thorough approach such as the A3 process

There is no reason to limit the number of whys to 5 or even go that far in some cases.

The countermeasures that come out of a 5 whys analysis are not expected to be implemented and immediately forgotten about. They are part of a plan that expects follow-ups, measurement and observation of the results.

The underlying causes of the analysis are not assumed to be the only causes or problems. The purpose of 5 whys is to limit over analysis. This may not make sense in life-or-death situations, but for most business processes it is appropriate and efficient to make decisions at a reasonable point in the analysis and move forward rather than investing a disproportionate amount of resources in that analysis.

The concept of a "proportional response" is important to lean. If the outcome of a problem is a patient's death, then the proportional response can be expected to be considerably more significant that just doing 5 whys.

If all a team does is ask 5 why questions then propose and implement a solution based on the last answer, this would be a pretty textbook example of a lean cargo cult.