From my experience with working on projects in industry, I would agree with the above posts that often during a project, it is necessary to go back to the planning phase to re-evaluate the project based on the current situation. Although the project management process is broken up into distinct phases, in the real world, some of these phases may blend together. In the project I am working on now, the timeline is changing almost weekly, resulting in the team going from executing on the current tasks to re-evaluation and re-planning based on the revised timeline. When this happens in a project, it makes the project run much less efficiently, because the team spends more time figuring out the timeline than executing. Changes to the timeline can either happen because of poor planning in the initial planning phase or because of unforeseeable events that caused changes, which cannot be avoided.