The Prioritized Approach was developed to address the highest common risks first in Milestone 1, the next highest risks in Milestone 2, etc. The Prioritized Approach provides a means to address risks quickly by first identifying where payment card data exists, and what parts of the network connect to this data.   That being said, each environment is unique, and organizations are encouraged to take a holistic view to payment card security and incorporate their PCI DSS compliance into an overall security strategy.