Why It Works
This game is based on numerous studies in cognitive psychology that have examined how we think about the future. When we ask the question "What will our product do?" we're left with an open-ended future, one in which every possible future is equally plausible. Of course, this isn't strictly true, and to answer the question we will pick a possible future and describe it. However, the lack of a concrete outcome means that we don't have to deal with the details of how our product will have done it. Others will tend to judge our answers as "hollow" or "lacking substance," because there is no requirement that this is actually the future that will materialize.
The results change rather dramatically when we alter the wording of the question. When we ask "What will our product have done?" we are thinking of a future event as one that already has occurred"remembering" the future. Because this event is "in the past," we must mentally generate a sequence of events that caused this event to have occurred. We not only have a more concrete idea of what the product did, we can begin to answer the question "How did the product do it?" Others will tend to judge our answers as more richly detailed, more sensible, and more plausible, precisely because if an outcome or future is thought of as already accomplished, it can be more easily described.
Time Frame of Action
This isn't to say that the event we envision will actually occur, or that each customer who plays the game will generate the same result. Actually predicting the future is not really the purpose of Remember the Future (although if you have success in doing this, please let me know). What is important is that Remember the Future enables you to not only understand your customers' definition of success, but also their understanding of how that successful outcome happened.