I found this great Lego ad yesterday on SlipperyBrick:
Sometimes relying on audience imagination can work, sometimes it does not.
  1. Sometimes it can work. Although adults might lose some of their imagination capabilities over time, it is still possible to get across visual messages with very simple graphics. Simple shapes, simple cartoons, even just creative typography. The mind will fill in the missing pieces
  2. Sometimes it does not work. The book Made to Stick introduces the concept of Curse of Knowledge. The presenter "hears"/imagines a tune in his head and taps it with his fingers on the table. All is perfectly clear to the presenter. All the audience can hear is.... someone tapping.