A Project plan often gives the impression that we know the steps we will take to achieve the given outcome. In practice, a Project plan is merely a logical sequence of tasks. It does not imply that we know all the tasks that the project team needs to execute. Further, it does not mean we know precisely how much time and effort the planned tasks may take. We do not account for people calling in sick, incompetence, team management issues, priority changes, or competing projects.
So, next time you come across the Project Plan, understand that it is a mere description of the sequence of tasks to reach the end goal. In practice, the Project Plan may need to be updated many times during the project’s duration. It is a normal evolutionary process.