Engineering is managing constraints and trade-offs. After satisfying basic system functionality, a workable plan must balance your cost, performance, schedule, and volume targets to develop a useful design. Below are some quick polls about risks and tradeoffs that are interesting to compare your last project with your peers.
source: Driving Innovation In a Time of Resource Constraints by Maureen Carlson at Appleseed Partners
Also here is one of our favorite Dilbert cartoons on project management. Dilbert.com