#33-Product Confusion Reveals Coupling

Products that are difficult to use or illogical in their design can seriously impede their value.  This episode will examine an example of such a problem, from the author's own personal experience with a new car.

Transcript

I bought a new car a few years back.

The next morning, I went out to my shiny new vehicle, got in, and started it. Once it was running, I tried to put it into reverse gear to back out of my driveway, but it would not go. The shift lever was stuck in “Park”. I was rather upset, it being brand new, even though logically the best time for a car to fail is immediately, while it’s still unquestionably under warranty. Still, I was not happy about it.

I called the dealer to explain, with some chagrin, the problem I was having.  "Ah, yes, that always happens," they said. This was not what I wanted to hear. Had I selected a car model that routinely broke its transmission?

That was not what they meant. "People are always confused about this model... and we always forget to tell them for some reason. To put that car into gear, you need to put your foot on the brake."

I was on my cell phone, so I tried it while the dealer was still on the call, and it worked.

"We sometimes just put our foot on the brake naturally when we start the car, so sometimes people do not run into this for a while," the dealer went on, "but invariably someone will call, within the first week or so, and report a failed transmission."

"Why did they engineer it this way?" I asked. The designer in me was curious.

"It is to make sure your foot is not on the gas pedal. People use their same foot for the gas and the brake, so if the foot is on the brake, it is therefore not on the gas.   Putting the car into gear while the engine is revving is extremely dangerous."

But later I began to think... why didn't they just hook a sensor up to the gas pedal? I reasoned that they did it this way because there was already a sensor on the brake pedal, to activate the brake light, and since there is no "accelerate light" they would have had to add something new to sense that the gas pedal was not depressed.   

I then thought about my grandfather, who was a farmer and learned to drive on a tractor where you use both feet, and my father who was a police office and trained to do the same.  This “safety feature” would do nothing to protect them.

This is bad coupling. The brake light system and the transmission do not, logically, interconnect in the user’s mind. My expectation did not include this as a possibility and the reason the dealer forgets to tell people about this is that it is no more logical to them that it is to me. The detail is routinely forgotten.  It was done in a way that was convenient for the engineers but was not at all helpful to the users of the product.

We need to take care to ensure that the way elements of our systems interact is logical and expected.  Donald Norman, in his fascinating and entertaining book “The Design of Everyday Things” points out that a well-designed system will make its proper use obvious and its improper use impossible.

This is another reason I recommend Commonality-Variability Analysis be done on all requirements.  One of the many things it reveals is illogical and unexpected coupling like this. 

Finally, it points out the fact that usability is the most important aspect of value in systems that are meant to serve people, which is all of them ultimately.  It is the “why” of systems development.

See my recorded webinar on Commonality-Variability Analysis:
https://www.projectmanagement.com/webinars/863805/commonality-variability-analysis