The Art of Project Management

2.4. Why schedules fail

Project schedules are the easy scapegoats for everything that can possibly go wrong. If someone fudges an estimate, misses a requirement, or gets hit by a bus, it's the schedule (and the person responsible for it) that catches the blame. If the nation's power supply were to go out for 10 days, or the team's best programmers were to catch the plague, invariably someone would say, "See, I told you the schedule would slip" and wag her finger in the schedule master's face. It's completely unfair, but it happens all the time. As much as people loathe schedules, they still hold them up to an unachievable standard. Even the best schedulers in the world, with the smartest minds and best tools at their disposal, are still attempting to predict the future—something our species rarely does well.

But if a team starts a project fully aware of the likely reasons schedules fall apart and takes some action to minimize those risks, the schedule can become a more useful and accurate tool in the development process.

2.4.1. Shooting blind from very, very far away

If a schedule is created during initial planning, hundreds of decisions that may impact the schedule have yet to be made. There will be issues and challenges, which no one can foresee, and there is no way an early speculative plan can possibly account for them. Until requirements are understood and high-level design is well underway, a project manager is too blind and has too little information to make realistic ...