Plans have two main purposes:
- We use them to direct the project work
- We use them to evaluate the project work
The work follows the plan, and yet it never exactly matches the plans. So, we revise the plans based on facts to get realistic outputs for the remainder of the project. When we do so, we also get the revised targets of the project; e.g., your project was initially planned to be done in 16 months, but based on the current information, your estimate is that it will likely be finished in 18 months. In that case, what would you do?