We have, in this chapter, gone through a step by step process of building a model by continually adding small pieces to an existing model. The advantage of this method is that you always have a working model. The disadvantage is that you can lose sight of the forest for the trees. It is always a difficult problem to determine when to stop adding. If you are not taking a broad view it is possible to add more and more detail without improving understanding. Building in small steps is a powerful approach, but you need review progress from time to time to see if the steps are taking you in the direction you want to go.
