Systems must change or become progressively less useful for a number of reasons:
1. The presence of the system changes the ways of working in its environment and this generates new requirements. If these are not satisfied, the usefulness of the system declines.
2. The business in which the system is used changes in response to market forces and this also generates new system requirements.
3. The external legal and political environment for the system changes and generates new requirements.
4. New technologies become available that offer significant benefits and the system must change to take advantage of them.