Anyone working in User Experience knows that it’s important to understand the context of your users’ environment and to design around that. For instance, an application designed for a busy police station where the users are constantly interrupted by unrelated tasks would take all those interruptions into consideration and help the users work around them. The latest The Daily WTF article is a perfect example of how external factors can affect a system.

To summarize, there was a minor glitch in an old punch card-based reporting application that was found by an accountant. The developer assigned to fix it tried everything he could think of, to no avail. Finally, he vowed to stay through the night until he had it figured out. During his late night, a cleaning lady came in.

“Sorry,” the cleaning lady said, picking up the hand broom she’d dropped. The developer’s attention turned to her while she swept up some dirt into a small pile. Nonchalantly, she reached into the punch card bin and swept the dirt onto one of the cards, picked it up and carried it to the trash, and threw away the card with the dirt.

This example illustrates the need for prevention poka-yoke devices, as discussed by Robert Hoekman, Jr. in his book Designing the Obvious.

Prevention devices are those that prevent errors from ever occurring. The hole in the rim of the sink that keeps it from overflowing is a prevention device. The user can leave the water running all he wants to - the sink will never overflow.

The punch-card-as-a-dirt-pan issue should have been prevented with some sort of poka-yoke device. Maybe they could have made the punch cards usable for one purpose only. Or, at the very least, make them a bit less accessible to the cleaning personnel. If your system depends on some outside factor, you better make damn well sure that you can count on that outside factor being used only the way that it’s intended to be used.


p.s. Robert also has a new book out, Designing the Moment, which I haven’t read yet, but look forward to reading.