TL;DR
In the last post, we gave you a critical thinking exercise: the root cause of my issue with balcony blinds. Today we present the root cause and critical thinking technique Occam’s Razor used for solving this issue.
The Community
I would like to thank the community for providing feedback on this exercise.
James Thomas
@qahiccupps Vice President at @AST_News. Founder of @Linguamatics. The organizer of CEWT. Author of When Support Calls. Sympathetic skeptic. Cambridge, UK qahiccupps.blogspot.com Joined December 2011
James gave his solution along (very important), explaining his critical thinking. As he is a sympathetic skeptic, I was very excited to read his answer.
Hi Karlo, I don’t have Facebook so I can’t comment on your blog š I spent a few minutes thinking about today’s puzzle and here’s my first response:
I think the problem is that the door blind gets stuck at the top when fully retracted.
The videos don’t give a good view at the mechanism for raising and lowering the blinds. It appears to be some kind of tensioned ribbon and when the door blind is stuck at the top it looks like the tension is lost.
I tried to make a mental model of what might be inside the box and thought of three things that I have seen in the past that have external similarities: car seat belts, retractable tape measure, and roller blinds with a pull-release action.
In all of these, I think, there is some kind of stopper (to govern the extent of movement) and some kind of spring (to provide tension). Moving past the stopper can cause problems with the tensioning.
So my guess is that there’s a stopper of some kind and you’re able to retract the blind past the stopper.
Here is the analysis of his solution.
On my blog, I use the Facebook Comments plugin. This is not the most effective solution because I know many people from the Software Testing community that do not use Facebook. But the Facebook plugin gives me out of the box and for free spam filter. The feature that I would need to pay for in WordPress. Also, spam paradise opens when you do not require users to be logged in, but requiring users to log in to the comments provider definitely lowers the number of responses.
I learned that I will also provide a link to the Tweet of a blog post for the next feedback.
As a skillful tester, James first provided the context: I spent a few minutes thinking about today’s puzzle. As software testers, our work should always be organized into the uninterrupted time-boxed session. By doing that, we maximize our testing effort. We are in the flow. Zeljko wrote about this in his blog post Books That Have Changed My Life. Also, you should check James Bach Session-Based Test Management.
James set a time box for his session of a few minutes. Adjective few is a problem for itself, because how much is a few? It is a small amount. We can assume up to ten minutes.
I created a video of a problem, and James identified it correctly:
I think the problem is that the door blind gets stuck at the top when fully retracted.
He used his observation skill of a video at his disposal.
The second observation is also correct. The ribbon lost its tension when the blinds were rolled up all the way to the top. It is also true that the video does not clearly show what the mechanism of the blind is.
James fired up his artillery :). He used the Mental Model critical thinking technique. Model of something that we can not see in the video. How do blinds roll up in the blind box? I also did not film what is inside a box because we need a tool to open the box. To help himself with the mental model, James is using the Comparable Products Heuristic [Back, Bolton]. He identified three comparable products:
- car seat belts
- retractable tape measure, and
- roller blinds with a pull-release action
He is using those three in daily life. We have two important parts of those products: stopper and spring. Spring provides tension, and the stopper function is to guard that tension by not allowing movement to pass it.
His solution: So my guess is that there’s a stopper of some kind, and you’re able to retract the blind past the stopper.
And the result is that blinds are stuck in the box.
The Solution With Occam’s Razor
a scientific and philosophical rule that entities should not be multiplied unnecessarily, which is interpreted as requiring that the simplest of competing theories be preferred to the more complex or that explanations of unknown phenomena be sought first in terms of known quantities
To use Occam’s Razor, we must first have several proposed solutions. James provided the first one. Let’s use Jerry Weinberg rule of three:
āIf you havenāt thought of three possibilities, you havenāt thought enough.ā
The second solution was actually the first solution proposed by the blinds specialist.
Blinds consist of lamelas:
His first guess was that some of the blinds Lamela’s are damaged, so they do not fit when rolled in the box. Here is the box with the correct Lamela fit:
Then he opened the box and found the solution. The box was too small to fit all the blind Lamela’s when fully rolled up!
But from proposed solutions, how could Occam’s Razor help us to identify the correct solution?
We identified the following blind attributes:
- stripe
- a stopper
- lamela’s
- box
What are the attributes of those elements?
- stripe => tension
- stopper => movement
- lamela’s => structure
- box => volume
What are the risks related to those attributes:
- Tension is lost
- stopper is broken
- Lamela is damaged
- Volume to small
What is the most simple risk?
Tension, stopper, and Lamela require mechanical damage, but box volume comes in combination with Lamela volume. Lamela volume is related to how long blinds are. The blinds’ length is determined by the height of my balcony door. The balcony door height is determined by the height of my room. And my room height is not standard for Croatian standard. It is like 10 cm above the average. Box volume to small does not require any force; it is people’s problem. Builders had to connect two related attributes, room height, and blinds box size. And they missed.
Conclusion
The simplest solution for a problem is one that involves human decisions.
Extra
After identifying the problem, blinds professional immediately called for comparable products: Do any of your building neighbors have the same issue?
My friend Boris recently moved into the building next to mine, built by the same company. And he has the same issue š
