Software Architect's Handbook

Law VII – Declining quality

As a software system evolves, its quality will decrease unless a concerted effort is made to maintain a high level of quality. Focus, discipline, and a rigorous effort must be sustained during the lifetime of the software system to minimize the number of defects that are introduced.

As more code is added to the system during its active life, there is the potential for an increase in the number of defects. Poorly designed enhancements may contain bugs or fail to satisfy some requirements. Maintaining the same level of quality is difficult as a software system increases in both size and complexity.