The purpose of design validation is to demonstrate that a product performs as intended. The usual route to this goal is showing that every item on the specification has been achieved, but it is not an easy path. The specification itself can create difficulty if it includes statements like "as long as possible" or the real horror "to be decided." Verification tests can reveal so many problems that the design must change to such an extent that earlier tests are no longer relevant. And there is also the practical difficulty of obtaining sufficient samples to test when the manufacturing engineers have not completed their standard operating procedures, the product design is not fixed yet, the component suppliers are late, and the marketing department has taken all the samples to show to prospective customers.