Basing a software project on an unrealistic schedule and the insufficient staffing and technical planning that result from it is tantamount to heading into the woods in November without a warm jacket. If a hiker gets into trouble, it's useful to know that a person can go for days without food but not without water. A successful software project establishes Explicit Priorities , so that if it gets into trouble it knows which features are essential and which can be jettisoned. Explicit priorities help to avoid the problem of wanting all possible features with the best quality in the shortest time with the least effort. They provide no guidance when the project needs to make tough choices.
Explicit priorities make the tough choices easier.
A common theme running through the Ten Essentials is that of hoping for the best but preparing for the worst. You wouldn't go hiking if you expected to break your leg, and you wouldn't start a software project if you expected it to run 300 percent over budget. In spite of your best hopes, however, you'd be foolish to go hiking without adequately preparing for the risks inherent in the activity. Active Risk Management is also a key component of successful software projects. As Tom Gilb says, if you do not actively attack the risks on your project, they will actively attack you.