Second guessing creative briefs

I read an article from a marketing person recently. They are involved in the creative industry and the article was about briefing a creative.
The take-out from the article was important from both the client and the creative expert perspective. It was that the client needs to be specific about what they want.
After reading that article I could not help but to test that theory. After some further consideration I have found that the statement, 'be specific' is not specific enough.

What if a client doesn't actually know what they need? This is likely the case when they approach a professional design studio for assistance in the first place.
Should a new prospect know what they need and exactly the way they want it presented, then they should really go to a finished artist or desktop publisher to obtain the communication item.
In theory, if we went with the original sentiment about the client being specific, then the designer wouldn't be the best person for the job. This idea has cycled about my little mind for some time and I have some conclusions after further consideration.
The client still needs to be specific - but they need to be specific about the areas where they are not sure how to proceed as well as where they are sure how they want to proceed.
If the client would like the designer to solve the challenge from A - Z - then they also need to be specific about that request.

Conceptual: Product design - one-push pizza cutter

Push down and cut your pizza with one downward movement. Cut into eight slices fast. When positioned in the middle of the pizza, all portions are cut equally. Best suited for pizza shops with lots of quick orders. The arms holding the blades are flexible springs. Depending on the materials and spring direction, the flexible spring may assist in the downward pressure when the arms spread apart. The central arm serves a dual purpose: it acts as a stationary stabilising element and as the initial central 8 way dividing cut. The round blade wheels then spray outwards from the middle to continue to cut the pizza into 8 slices in one downward push. The central arm moves up the handle as the arms flex away from the centre. COncept design: ©Copyright Nicholas Girling 2009 All Rights Reserved.