Session 15

Uncertainty in Design


Environment, Technology, and Society

Exercise: Uncertainty in the Design Process


You have read quite a bit about the design and use of products from the user's perspective. It seems that many products are not designed well enough, or at least not with enough thought about usability.


  1. To consider the role of uncertainty in product development.


Work in teams of three or four people based on the number in the upper right hand corner of this page. If yours is an odd number, your magic word is for. If yours is an even number, your magic word is against.

A book on design, technology, ethics, and responsibility once proposed the "Ivory Snow theory" of product development. The gist of this theory is that "perfect design is an oxymoron" -- that no product can be better than 99.44% good. (The name of the theory and the particular percentage refer to a longstanding slogan for Ivory soap, which Procter and Gamble advertised as 99.44% pure.)

This theory might be used as justification for good design or bad design, depending on how one chooses to apply it.

Construct a convincing argument <your magic word> the Ivory Snow theory. Be sure that your argument...

I realize that you may be put in the position of arguing for a position that you do not personally hold. Welcome to the world. Make that a part of the fun!

At the End

  1. You argue your case in class.
  2. Your group submits its write-up.

Summary from Exercise

Class discussion considered the continuum between doing nothing and doing a perfect job. Clearly, most of our efforts will fall somewhere in between. Some companies have a reputation for releasing products relatively early the continuum, and some of you thought this a wise strategy. It gets your product to the market earlier, perhaps first, and takes advantage of massive parallelism in testing the product. Such a strategy is often more cost-effective than doing in-house testing with a small team, and it may even benefit the customer who has a (nearly correct) product sooner and can thus begin the long road to integrating it with other products.

In what circumstances of the theory is Ivory Snow a pragmatic one, and in what circumstances is it merely a rationalization of sloppiness?

Products for which Ivory Snow seems to make the most sense: entertainment packages; anything where the cost of failure is relatively low, say, word processing. (Don't tell that to the user of a word processor who has just lost several hours of work.) We must keep in mind that the person to judge cost of failure is the user, not the developer. So we need to ask ourselves: Who are the users? How do they judge and handle failure?

Products for which Ivory Snow does not make sense: any device with life-critical functionality; complex systems in which a small error can propagate into a large error, especially when the observable failure is no longer proximate to the cause of the original error; military applications; financial applications!?

Another interesting point that students have raised in the past: The theory makes sense when the developer controls the environment in which the product will be used, say, custom hardware or a company-controlled client group. It doesn't make sense when the environment is out of the developer's control. (How often do you imagine that is?)

The bottom line for some of you seemed to be: You can't make perfect products, so weigh the costs of failure against the costs of improving the failure rate. (Someone else equated this to joining the Mafia. :-)

On Perfection

The book from which I borrowed the Ivory Snow theory is Richard Epstein's The Case of the Killer Robot, a text on ethics and repsonsibility for computer scientists. In his discussion, Epstein often uses a quote that I frequently use: "Perfection is the enemy of the good." But we differ in how we mean it. Epstein uses it in a pejorative way -- that such a lackadaisical attitude can lead to product failure. I'd like you to think about how one might make this assertion in a serious but pragmatic way. When have we done enough? What standards do we use to make the judgment?

"The perfect is the enemy of the good." By this, people often mean that striving for perfection results in the product never being finished. (There is always one more improvement to make...) But I think that there are two other senses in which this adage is true.

Design is about trade-offs. That is true in terms of design features and in terms of business, legal, and ethical goals. Optimizing any one goal is not usually a good idea, even when possible. Pretending that we can design perfect products can lead to bad results -- but using that as an excuse for bad design can lead to worse.

On Uncertainty

Ivory soap turns out to be a great example for this discussion for another reason: its unique "floatability" resulted from an error that an employee made during the manufacturing process! Check out this web page on the legend. You can also read a more marketing-driven history at

Students Summaries

Eugene Wallingford ==== ==== November 18, 2003