That brings us back to the question – Is there anything like “idea!”? Can there ever be a state in the journey of a product where success is guaranteed? I don’t think so. In fact, the euphoria around the market success can be a sure shot sign of some untested assumption being overlooked. The only time an idea enters “idea!” state is while it enters the sunset zone – and the certainty is that of death! Of course, in the case of iPod, even that is uncertain in the near future.
In short, no matter how fantastic your idea is, don't be in a hurry to treat it as an "idea!". Treat it as an "idea?" and be clear about the key untested assumptions at every stage of its evolution.
source: Steve Jobs comment on the future of iPod that he presented to the board is mentioned in his biography "Steve Jobs" by Walter Isaacson, page 465.