When you create a project plan, think of yourself as a general contractor trying to build a new home. As the general contractor, you’re not necessarily going to physically perform each task. By yourself, you probably would not dig the trenches, mix cement, lay blocks, plumb pipes, wire the electrical, frame the house, set the drywall, paint, lay carpet, install siding, shingle the roof, and many of the other tasks which are often associated with building a house. You either have crews of specialists that are necessary to complete the tasks… or you have sub-contracted different parts of the project to different people.
What would happen if the roofing contract came before the foundation was built? He’d have to go home… or you’d have to pay him until everything else was done and he could do the roof. If the excavator doesn’t complete his task at the beginning of the project… and waits until toward the end of your 180 day contract… nothing else gets done. The general contractor won’t be in business long if they can’t optimize their resources… which we refer to as Project Management.
With any project, it’s basically the same thing. There is a natural order and sequence to everything, and the absolute best performance you can hope for is called the critical path. Why is it critical? It’s critical because anything that get’s delayed on the critical path will automatically have a ripple effect and delay the overall project by the same amount of time unless you have sufficient slack in the schedule. Without slack in the schedule to absorb a delay, if an item on the critical path is a week late, then the project is a week late. That is barring some heroic effort to reduce the time required to complete a downstream task on the critical path.
When managing a project, make sure you know the critical path. Manage the critical path, and you will manage the project. If other tasks not on the initial critical path become delayed… they could easily become the new critical path… and should be managed appropriately.