While they're engaged in any activity they are both having and not having fun playing the game. Not until the random rewards are given do they actually know which was the real case.
EDIT: Kage Goomba, your idea of not opening the box is a good one. How about calling the error message when a person gets kicked to orbit [b]just befor[/b]e finishing an activity -- "Schrödinger's Cat"?
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This is still true. People depending on their rewards in game rather than on the actual enjoyment of their time spent.