Ideally, when you have finished with each change, the system will have the structure it would have had if you had designed it from the start with that change in mind. To achieve this goal, you must resist the temptation to make a quick fix. Instead, think about whether the current system design is still the best one, in light of the desired change. If not, refactor the system so that you end up with the best possible design. With this approach, the system design improves with every modification.
