Practice
Most product work fails somewhere between the idea and the tooling. A concept survives the pitch, then meets a wall thickness, a draft angle, a supplier who has never made that radius - and quietly becomes something else. Our job is to make those collisions happen early, while they are still cheap.
That is why we take the whole arc rather than a slice of it. Research tells us what the product has to be true to. Sketching gives us breadth. CAD, CMF and physical prototyping resolve the one direction that earned it.