As time goes on, modifying production software tends to get more difficult and expensive. Changes add complexity, and complexity usually calcifies the code base, making it brittle and easy to break. Far too often companies are startled to discover that their software investment has turned into a tangle of unmanageable code. But this doesn't have to happen. The best software products have been around for a decade or more, and every useful product of that age has been changed regularly over its lifetime. These products have architectures and development processes that build change tolerance into the code. All code worthy of the name software should be designed and built with change tolerance in mind.
