Jumping in and immediately starting to build the product, even if it does get completed and ship, is almost guaranteed to produce a mediocre product in which there is little innovation or market differentiation. When you have only one kick at the can, the behaviour of the entire team and process is as predictable as it will be pedestrian.
—Bill Buxton in Sketching the User Experience
Buxton writes in this passage on the impact of iterative sketching on risk, exploration and innovation.