The document discusses how ERP systems quickly become legacy systems after implementation due to their inability to easily adapt to changing business needs over time. ERP systems reflect the business processes and data structure at the time of implementation but do not allow for flexibility as the business evolves. As a result, supporting outdated business practices in the ERP system becomes costly and prevents agility. The complexity of ERP systems, including relationships between millions of data fields and integration with other systems, makes any changes extremely difficult and expensive. Thus, the document argues that ERP systems effectively become legacy systems from the moment after their initial implementation.