Why is resource management significantly more difficult in a multi project environment?

Project management questions

1. Why is resource management significantly more difficult in a multi project environment? What are some rules of thumb to help project and program managers better control resources across several simultaneous projects or programs?

2. Reflect on what you learned from this project management course. Click on Integrated Program Management site:
https://www.acq.osd.mil/asda/ae/ada/ipm/index.html
explore the various links and screens. What does the size and diversity of this site tell you about the acceptance and use of earned value for programs and projects in organizations today?