The evil circle principle :
If requirements are unclear, incomplete or wrong, then the architecture will be equally wrong.
If the architecture is wrong, then our cost estimates will be wrong.
If the cost estimates are wrong, then people will know we are badly managed.
If the high-level requirements and architecture are wrong, then the detailed design of them will be equally wrong.
If the detailed designs are wrong, then the implementation will be wrong.
So we will end up re-doing the entire project as badly as the last time, because somebody will cover up the initial failure, and we will presume that the methods we used initially were satisfactory.