Refactoring toward deeper insight

Success developing useful models comes down to three points:

1. Sophisticated domain models are achievable and worth the trouble.
2. They are seldom developed except through an iterative process of refactoring, including close involvement of the domain experts with developers interested in learning about the domain.
3. They may call for sophisticated design skills to implement and to use effectively.

Eric Evans, "Refactoring Toward Deeper Insight", in Domain-Driven Design: Tackling Complexity in the Heart of Software, 188.