Question

A simple and effective concept from Toyota is Poka-yoke, or mistake-proofing. Products and Interfaces are context-sensitive — that is, products and interface features have a particular purpose , but I’m curious if you can share any generic context-agnostic approaches to mistake-proofing, or Poka-Yoke? Principles of Poka-yoke you can apply to anything; to any product or interface?

Answer

An interface is humane if it is responsive to human needs and considerate of human frailties.  We make mistakes.  No matter how hard we try to concentrate and prevent errors, errors will happen when our concentration wanes or when we are forced to do something that is beyond our cognitive abilities like multi-tasking: the act of consciously thinking about two things at once — and, with the use of Queueing Theory & Little’s Law, we learn that multi-tasking leads to lower productivity.

Poka-Yoke is an excellent method of making a process more efficient and humane by being considerate of human frailties: we won’t always be thinking about which way a part fits in, so design the part in a antisymmetric way so that it can only be installed correctly.

Shigeo Shingo, the originator of poke-yoke, wrote “Defects arise because errors are made; the two have a cause-and-effect relationship…yet errors will not turn into defects if feedback and action take place at the error stage”.  In other words, users make mistakes, but those mistakes are detrimental only if they aren’t corrected immediately.  One context-agnostic principle of humane interface design is summed up in the mantra “Never Use a Warning When You Mean Undo“.  If you make a mistake, no big deal.  Just undo it.

For example, a common Poka-Yoke style method is to cover an important switch so that it cannot be bumped accidentally. But, what happens if you use that switch all the time? You’ll either leave the cover open or flick-the-cover-open-and-flip-the-switch as a single gesture. In the computer world, we often have the advantage over the real-world in being able to undo. So that even though you just ran the smash-the-car-into-the-wall safety test while the technician was inside, you can just go back to the way it was before.

If Poka-Yoke was practiced more in interface design our lives on the computer would be a lot less stressful.

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