Reading Usable Help
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Gordon R. Meyer
Changes disrupt knowledge
Author Wendy McClure, in her book The Wilder Life: My Adventures in the Lost World of Little House on the Prairie, describes her experience with using a keyless automobile ignition:
Then the next day I couldn't figure out how to start the rental car again, because instead of a key it had a button, and even though I kept pushing it the engine wouldn't start, and this odd little lumpy icon would light up on the dashboard with the word BRAKE. After about ten minutes of fiddling with the parking brake, I looked closely and noticed that the lumpy icon actually depicted a foot on the brake pedal, indicate what I was supposed to do when I started the car, which of course I would have done automatically if I'd just had a key and not this weird button completely confounding my intuitive knowledge of how to start a freaking car. (Emphasis as in original.)
The lesson here for instructional designers is that useful one word error messages are hard to write, and that introducing a radical change in the middle of an established procedure may lead users to conclude that the entire procedure has changed.
I had a similar experience with my Volkswagen New Beetle. One day the car seemed completely dead. Turning the ignition key seemingly did nothing at all. In reality, as the car mechanic later pointed out, when I inserted the key a small icon depicting a key flashed on the car's LCD display. What was wrong was that the security chip embedded in the fancy-pants ignition key had become disassociated with the car's computer, so the key could no longer be used to start the car. That's what happened, but the user experience of this was completely opaque. The fault was the unobtrusive, wordless error message and my failure to consult the troubleshooting section of the owner's manual; I assumed the problem was a failed starter motor.
If you're curious about Ms McClure's book, I invite you read a review at my personal blog.