"Designers must try to avoid modes, but if necessary, equipment must make it obvious which mode is invoked." #readingToday

Mode error is really design error. Mode errors are especially likely where the equipment does not make the mode visible, so the user is expected to remember what mode has been established, sometimes hours earlier, during which time many intervening events might have occurred. Designers must try to avoid modes, but if they are necessary, the equipment must make it obvious which mode is invoked. Once again, designers must always compensate for interfering activities.

Design of Everyday Things Revised, Don Norman