Warning messages are surprisingly ineffective against mistakes {even nice requests, such as the one shown in Chapter 4, Figure 4.6, page 143}. Was this a mistake or a slip? Both. Issuing the "close" command while the wrong window was active is a memory-lapse slip. But deciding not to read the dialog box and accepting it without saving the contents is a mistake {two mistakes, actually}. What can a designer do? Several things: • Make the item being acted upon more prominent. That is, change the appearance of the actual object being acted upon to be more visible: enlarge it, or perhaps change its color. • Make the operation reversible. If the person saves the content, no harm is done except the annoyance of having to reopen the file. If the person elects Don't Save, the system could secretly save the contents, and the next time the person opened the file, it could ask whether it should restore it to the latest condition.
( Donald A. Norman )
[ The Design of Everyday Things ]
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