Design so that the wrong action is physically impossible, rather than discouraged by training or attention.
Shingo's principle, developed on Toyota lines: a fixture that will not close unless the part is the right way round removes a class of defect entirely, where a warning sign only reduces it. The design question is not how to make people careful but how to make carelessness harmless.
In practice
- A connector that only fits one way ends a fault the training slide had failed to end for six years.
- A form that cannot be submitted with the date field empty removes the query the helpdesk raised weekly.
- Further reading
- Wikipedia
- Subject
- Design & Systems
- Essay
- Rules of thumb for building things that work