In the engineering and manufacturing tradition that's been in place for centuries you design and develop your product, testing and verifying it as you go, and then you manufacture and sell it on to a user. At various stages during this process there are "feedback loops" that inform the design and development of future products. So it may emerge, for example, that the market wants some particular feature or doesn't much like another, or that a material has properties that make the product unsuitable, or that manufacturing can be simplified or made more economic by a design change.
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