A fundamental of managing projects is first to plan and then to accomplish. Of course, good project management is a lot more complex as we shall see shortly. In the simplest of terms, if you do not know where you are going you neither know how to get there nor even when you have arrived!. Moreover, it doesn't really matter which road you take nor how long it takes to get there.
So a good project plan is like a route map – the destination is clearly spelled out and the best way to get there is chosen before starting.