I agree with @srg36 that even if you use project management tools like Pert charts, Gantt charts, there will still inevitably encounter pitfalls, but you will be able to more effectively manage these scenarios with these management tools. As Dr. Simon mentions in lecture, it is important not only to schedule the tasks but to account for costs and resources before the tasks are known. The common pitfalls that arise in the planning phase in regards to costs; making up costs before you know the tasks, estimating costs without having planned the tasks or have done your research, and not accounting for risks and contingencies. Similarly the common pitfalls that arise in regards to resources include as @cdj24 mentions; not accounting for vacations/holidays, contingencies, other projects, and making commitments before tasks are known. Overall, I agree with @srg36 that this can managed effectively by having a robust Gantt chart so that you can adjust as necessary and have an up-to-date timeline on tasks/sub-tasks to manage the project. As Dr. Simon mentions MS Project has the ability to take into account holidays/vacations so there are ways to address and mitigate these common pitfalls.

In the PMBOK guide Chapter 4 provides an overview of the Project Integration processes which include; Developing a Project Charter, Developing a Project Management Plan, Directing and Managing Project Execution, Monitoring and Controlling Project Work, Performing Integrated Change Control and Closing the Project or Phase. I think Figure 4-5 is a Data Flow Diagram of the intricacies of developing a Project Management Plan. For example, this includes; Defining Scope, Creating WBS, Determining Budget, Developing Schedule, Plan communications, etc.