Why does the production stage need to be more predictable than the engineering stage?

Question

Why does the production stage need to be more predictable than the engineering stage?

Answer 1

In the engineering stage you are solving problems within a limited period of time.  Problems are unpredictable and allowances are made.  In production you are executing a plan for a sustained period of time.  The problems should have been solved in the engineering stage.  If the plan allowed to much unpredictability it would be unaffordable.  If the plan encountered too much unpredictability it would fail.  

Answer 2

The production stage is the end product of the engineering stage. When in the production stage you have already invested a great deal of capital and time. Bad planning here cost, it can't just be changed on paper.

Answer 3

Production stage has to be more predictable because in production you can't ensure who the user will be. In the engineering stage you still have the right engineering ability and resources around to fix the issues that come up. In production most of that engineering knowledge is not available, and here unpredictability equates to failure.