The critical path method (CPM) is considered the industry standard for managing projects. Government contracts frequently require developing and maintaining an incredibly detailed critical path schedule. CPM is at the core of all the best-selling project management software. Program Management Offices are adorned with large plots of project schedules depicting the network diagram and the critical path. So, if it is so widely used, then why are many projects late, over budget, and dissatisfying customers? There are several reasons why CPM fails so often:

1. Task durations have risk mitigation built-in. Success with CPM hinges on knowing the task durations. The most common method of determining task durations is to solicit input from each task manager or key performer. Not wanting to be blamed for getting the project off track, people generally include a "buffer." However, the duration of the buffer is not standard from individual to individual so when executives compress tasks to meet mandated milestones they often shorten the tasks with the minimum amount of buffer. Carefully consider the duration of ALL tasks AND the estimated hours to perform.

2. Task durations vary. Task managers and key performers evaluate task durations differently. Some input the actual calendar time they believe it will take to accomplish the task, and only that time. Others add time. For example, some task managers allow for realistic durations because they understand they may not be able to work on the task immediately or dedicate all of their time to the task because of competing priorities. Others are misled and miss deadlines because they fail to take into account the teams' availability to work on a specific project.

3. Commitment. Just because a task is on the critical path does not necessarily mean it will be accomplished. A task will be completed only when the responsible individual understands it is their task, it is on the critical path, and they promise to complete it.

4. Interfaces. Planners are responsible for developing durations for their assigned tasks but the project manager is responsible for delivering results. So who is in charge of ensuring that the order and the dependencies are correct? The PM. If PM is not confident making those calls in isolation, involve the task managers in the overall planning process.

5. Communicate. People need to know when they can begin work. Task performers cannot start tasks just because it says so on the master schedule. They can only commence when all predecessor tasks are complete. Many times they are never told to start. Likewise, problems are often not communicated to downstream performers allowing them to adjust their own work schedules and priorities to accommodate the delays.

In summary: remember that task starts and stops are uncertain; investigate every level of effort for every task on the critical path to identify buffers and adjust them accordingly; make assignments only when work is ready to be performed; involve key managers in the overall planning process to better understand dependencies; and, communicate frequently.