To have a project accelerate as development proceeds—rather than get weighed down by its own legacy—demands a design that is a pleasure to work with, inviting to change. A supple design.
Domain Driven Design, p244
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You can't expect people to want to improve your software if its foundational design is sloppy and tightly coupled. The model with which components of code within the same application interact with each other is just as important to its robustness as it is to its future maintenance and interaction with other software. Inward and outward, design even at the "internal details" is of utmost importance.
