An exercise in thinking.
Give following instructions: Cut a stripe off a piece of paper and give it one twist. Glue the ends together. Cut the strip in half.
Before users cut the strip in half, ask for the expected end result.
The end result is surprising for most users: The don't get two strips, but one large and thin strip.
Learning outcome: Results in the real world are often not as are expected. Prototype and test before you implement.