Indeed, it is rarely the case that the first idea that comes into the head of a design engineer is the best one. Da Vinci previewed every painting with a number of sketches, and Edison tried more than 1000 light-bulb filaments. As to the first question, Reinertsen argues that you should not start a project unless you intend to finish it. Experience with the auto industry suggests that he is half right. Toyota and its major suppliers are considerably faster than their competition, while producing higher quality designs with less engineering investment.
Every project goes to the finish.
Importantly, multiple concepts are maintained not only at the system level, but also at the subsystem level. This works in part because it provides redundancy, and therefore reliability, in the development process. By the end of the process, we have killed the weaker ideas through the simplest, cheapest, and fastest tests or analyses. And we have learned enough about the surviving ideas to be sure that they will work. Unfortunately, the more innovative the idea, the more difficult it is to tell whether or not it will work without doing some development.