The basic principle of IPM is plan the work and then work the plan. When IPM principles have been followed, the project is well planned in detail by the time the sponsor signs off on the complete statement of work and the baseline Gantt chart. All of the task leaders for the project have been involved in the planning and now understand the plan. All have or have ready access to the complete and detailed basic Gantt chart and the statement of work. Now there is nothing to it. The team proceeds to follow the plan and to complete the project to specifications, on time and within budget.
Strangely enough, this is very often not the way it happens. After having carefully planned the project, many task leaders and task workgroups forget that they have a plan. A few workers on the project are committed full time to the project from beginning to end. Most have other things to do other things that generally are not as well planned and scheduled as their project commitment. These workers may truly intend to do their tasks as scheduled. But, if it is not going to start for some weeks or months, they may lose track of their commitment to a start date. When the start date does arrive, they are in the middle of another effort and do not want to drop what they are doing to begin the project's task. Therefore, they will do the project task as soon as they finish what they are presently doing. (This is something for risk analysis to consider.) This posture, on the part of one or several task leaders, can blow the project plan apart.
There are many variations on why task leaders are not ready or willing to start their tasks at their committed time during planning. Some, who contribute enthusiastically to creating the plan, just never believed it was real; it is just a document that they can refer to as they work through the project. "But you never really expected it would actually happen the way we planned it, did you?" is their way of thinking.
The project manager must be aware that this attitudes exist among at least some of the project team. He or she also must realize that his or her job is not just to facilitate the creation of a good project plan; it is to make sure that the team works the plan and that each team leader is prepared to start his or her team's task as soon as the predecessor task(s) is finished. It is to make sure that the team approaches the task with due diligence. It is to make sure that each team leader keeps risk contingency plans in mind and is prepared to use them whenever warnings emerge during the task effort.
The project manager's job is to get the job done! THERE IS NO SUCH THING AS A GOOD EXCUSE! This means that he or she must have a thoughtout scheme for how to manage the project day by day and how the tools that he or she has available to manage this project will be used to make the plan work. This all begins at the project launch, which should take place at a meeting the day after the sponsor signs off on the project. All project team members must attend this project launch meeting.