We need to adopt the attitude that the internal structure of a system will require continuous improvement as the system evolves. Refactoring — improving the design as the system develops — is not just for commercial software. Without continuous improvement, any software system will suffer. Internal structures will become calcified and fragile. In a surprisingly short time, the system will cease to be useful.
From the Book Lean Software Development: An Agile Toolkit, ISBN 0321150783