Traditional PM is based on 2 core concepts:
This implies that a project must be managed by one Project Manager:
And this is where many enterprises fail. For a number of reasons, either more than one person is put in (partial) charge of the project, or none at all (trusting in everybody's sense of responsibility, etc. etc.).
In both cases there is a deadly sin: there is no Project Manager.
A Project Manager has a number of tasks, the main important ones being planning and controlling the project and co-ordinating the Project Team.
Obviously, for projects of a certain entity it becomes impossible for one person to take direct care of the planning and control functions. In which case, planning and control gets broken up and delegated to Project Team members, while the Project Manager co-ordinates them and keeps an overall view of them (more »).