Tesler’s Law of Conservation of Complexity:


In today’s post, I am looking at Tesler’s Law of Conservation of Complexity. Larry Tesler, who came up with the law, worked at Xerox PARC, Apple, Amazon, and Yahoo in different capacities. He was one of the brains behind “cut/copy and paste” functionality in word processors. The basic premise of the law is as follows:

“Every application has an inherent amount of irreducible complexity. The only question is: Who will have to deal with it—the user, the application developer, or the platform developer?”

This is an important idea in the user interaction with a software application. One of the best examples to explain this further comes from Dan Saffer’s excellent book, “Designing for Interaction.” Think of the email application. It needs a “From address” and a “To address”. Without either of these two items, the email cannot be sent. All, if not most, email applications will automatically populate the “From address”, thus not requiring the user to enter it all the time. This “complexity” was addressed by the software application designer. As Dan put it; The complexity isn´t gone, though – instead, some of it has been shifted to the software.

Larry Tesler was a firm believer that the user interaction is almost as important as the application itself.

In the early days of our field, when I worked at Xerox PARC, the idea of user interface consistency was new and controversial. Many of us realized that consistency would benefit not only users, but also developers, because standards could be encapsulated in shared software libraries. We made an economic argument: If we establish standards and encourage consistency, we can reduce time to market and code size.

I postulated that every application must have an inherent amount of irreducible complexity. The only question is who will have to deal with it.

Because computers back then were small, slow and expensive, programs were designed to be compact, not easy to use. The user had to deal with complexity because the programmer couldn’t. But commercial software is written once and used millions of times. If a million users each waste a minute a day dealing with complexity that an engineer could have eliminated in a week by making the software a little more complex, you are penalizing the user to make the engineer’s job easier. (Source: Dan Saffer Interview with Larry Tesler in “Designing for Interaction”)

With this law, we are not trying to make things simple. A complex situation requires that the solution is also complex. This goes back to Ross Ashby’s Requisite Variety principle – “only variety can absorb variety.” The variety is described as the number of possible states of a system. If the “problem” requires that you need 7 states, then the solution should address it by providing at least 7 states. Tesler’s law recommends that we keep this complexity away from the user and absorb it at the programmer’s side. This makes the user interaction favorable leading to a positive user experience. We should focus on making life easy for the user.

The user experience is related to the cognitive load that is placed on the user. The application should try to minimize this load to avoid any potential errors or slips. The more steps a user has to complete, the more likely an error can occur. This may not be a big problem if we are drafting an email, but if the user is a pilot, then the whole scope of the problem changes. Providing a consistent interface and eliminating unnecessary actions minimizes the cognitive load on the user, and ultimately reduces the errors and slips by the user.

This makes me think about the concept of “muri” in Lean. “Muri” refers to the unnecessary burden on the operator or the system. Muri always leads to Muda (waste). When we are designing an interface for the operator at the gemba, we should try to make that interface as user-friendly as possible in order to minimize the cognitive load on the operator. As Tesler’s law suggests, the designer should absorb the complexity so that the operator does not have to worry about it. Many of the concepts of user experience are applicable in designing a work station. The focus is not to make things “simple” but to match the complexity needed and embed it in the interface in an efficient and effective manner so as to reduce cognitive load on the user. This leads to a satisfactory experience for the user and minimizes the chance of errors. When trying to save money, don’t try to cut corners with technology. Think of it from the time saved by the operators and the minimization of cognitive loads leading to better products and processes.

The other side of the coin is an elaboration that Bruce Tognazzini made with Tesler’s law. Bruce is another great User Experience pioneer. He postulated that when we remove the complexity from the user, the user will try to attempt more complex tasks. The reduction in cognitive load on the operator leads to the user engaging in more ideas for improvements that ultimately leads to better and more efficient operator interface. This may also lead to better cross training, and increase in employee morale. There will be more interest in engaging in the improvement culture, which is at the heart of lean.

I will finish with a great Don Norman story about user experience. Don Norman is the director of The Design Lab at University of California, San Diego, and has written numerous books of designing and user experience.

Don Norman is a proponent of designing things so that the conceptual model becomes easy for the user. The conceptual model is the mental model that the user creates when interacting with a designed object. The conceptual model allows the user to understand how the object functions. Don talks about the experience his son had with the first Macintosh computers. At that time, the file storage was mainly done with floppy drives. His son was trying to save a file and got the error message. “Sorry, there is not enough room to save your file.” His son looked at the folder and saw that there were many folders within the folder and they were arranged in a haphazard fashion. His son using the conceptual model he had came up with a solution – rearrange the folder icons in the folder towards the left so that “there was lot more room on the right side.” He tried again saving, and got the same error message. He was puzzled because the folder obviously had more room now. Don stated that his son was using the wrong conceptual model. The “room” on the picture on the folder was not the same as the “room” on the floppy disc.

Always keep on learning…

In case you missed it, my last post was Kufu Eyes:


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