An anecdote of how someone saying, "Say, a paintbrush is a pump" helped people solve a technical problem through use of this Generative Metaphor.
> Some years ago, a group of product-development researchers was considering how to improve the performance of a new paintbrush made with synthetic bristles. Compared to the old natural-bristle brush, the new one delivered paint to a surface in a discontinuous, ‘gloppy’ way. The researchers had tried a number of different improvements. They had noticed, for example, that natural bristles had split ends, whereas the synthetic bristles did not, and they tried (without significant improvement resulting) to split the ends of the synthetic bristles. They experimented with bristles of different diameters. Nothing seemed to help.
> Then someone observed, ‘You know, a paintbrush is a kind of pump!’ He pointed out that when a paintbrush is pressed against a surface, paint is forced through the *spaces between the bristles* onto the surface. The paint is made to flow through the ‘channels’ formed by the bristles when [those] channels are deformed by the bending of the brush. He noted that painters will sometimes “vibrate” a brush when applying it to a surface, so as to facilitate the flow of paint.
> The researchers tried out the natural and synthetic bristle brushes, thinking of them as pumps. They noticed that the natural brush formed a *gradual curve* when it was pressed against a surface whereas the synthetic brush formed a shape more nearly an angle. They speculated that this difference might account for the ‘gloppy’ performance of the [second] brush. How then might they make the bending shape of the synthetic brush into a gentle curve?
> This line of thought led them to a variety of inventions. Perhaps fibers could be varied so as to create greater density in that zone. Perhaps fibers could be bonded together in that zone. Some of these inventions were reduced to practice and did, indeed, produce a smoother flow of paint.
> Paintbrush-as-pump is an example of what I mean by a Generative Metaphor.