"Nobody plans to fail, they only fail to plan." These tend to be the first words you hear after missing some obvious element in an otherwise brilliant solution. A good friend of mine once had to call the police to open the locked trunk of his car. Seems the last thing he did before shutting the lid was to place his keys on his coat, which was in the trunk. He had a back-up key, which was in his wallet... which was in his coat. You get the picture.
The Flintstones always made me laugh. At the end of every episode, Fred would attempt to put the cat out. The cat (apparently smarter than Fred) would immediately jump through the open window beside the door. This explains why Fred never became an architect.
As architects, it is our mission to plan for the unexpected, but sometimes we completely over look the normal, the routine, the expected. Designing great solutions often requires that we understand the problem in context.
I love this picture and use it frequently to make a couple of points. First, take a close look and make sure you can spot the gate arm that is supposed to stop cars from entering and exiting the parking lot. Now note that as a car enters the lot (from the top of the picture moving downward), there is no place to insert a ticket or otherwise identify the car or driver. Therefore, the gate must just open automatically. For everybody. Well, maybe this is a heavily trafficked area and the gate serves as flow control. Hmmm, the serenity of the narrow streets and grassy lawns would seem to suggest that traffic congestion is not an issue.
Of course, there is the obvious indication that the gate merely impedes traffic for no apparent benefit, as evidenced by the turf marks clearly seen in the light snow. Good designs just work. This one doesn't. No one planned for this gate to be useless, in fact, there may even be a good reason for it. But, this particular design fails. (BTW, If you are interested in application security, this would be a good example of how a bad design only considers the users that want to follow the rules.)
Oh, the lessons that can be learned from this one photo are nearly endless. How about this; when a important task is at hand (in this case, maybe... getting home?), people tend to use the path of least resistance. Think about the solution you are designing right now; is the use of the solution (in the eyes and hands of the user), the path of least resistance?