Once a large software legacy is built up, accumulated design problems and the intrinsic complexity of integration combine to make it more and more difficult to execute clean design. A team may set out to design a new piece of software using a domain model, and at first they are focused on strategically valuable new features. In collaboration with business innovators, they outline a new vision of some part of the domain. They distill a model and design the new functionality.

Of course, the new functionality calls for integration with existing functionality. As the new vision is stuck together with a messy legacy system, lots of expedient compromises are made. Perhaps the new work must also be integrated with an external system and the introduction of these external elements leads to loss of clarity in the model. In response, the team may try to redesign or replace more of the legacy system, and the scope expands, and the work bogs down. There are various ways this may happen, but they lead to the same place. The focus on strategic value is lost, and a fresh and clear approach to the problem is muddied to the point that it has no impact.