Choices cause stress. The more serious and irrevocable the choice, the more stress it causes.
Ambiguity compounds stress by making the path unclear. When it’s not clear what will happen when you press a button, or whether “undo” is possible, you have to think harder and longer before taking action.
Don Norman’s classic The Design of Everyday Things gives us the textbook example of design ambiguity: a stove where the controls don’t “look like” the burners.
Great products eliminate ambiguity.
iPhone controls are intuitive because the round button only takes you to the “home screen” application launcher. Once you’re inside an application, the control context switches to the touchscreen.
On the Blackberry Storm, you constantly have to switch between the onscreen touch controls and four physical buttons. These vestigial buttons force you to make unnecessary decisions dozens or hundreds of times a day.
Browser controls are only on the touch screen.
Input context constantly switches between the physical buttons and the touch screen. Even worse, the “back” button is “browser back” but becomes “back to home screen” when you run out of browser history.
Users can learn to compensate for ambiguous design, but the experience will always pinch like ill fitting shoes.