One of the best quotes I have come across was from Robert C. Martin. For me this quote reemphasizes the ideal to keep things simple and stop when a concept is working, simple and explicit. It might not be perfect, but some times OK, is good enough.
> No matter how much time you spend trying to figure out the perfect software > structure, you will always find that the customer will introduce a change > that violates that structure. There is no escape from this. There are no > perfect structures. There are only structures that try to balance the current > costs and benefits. Over time those structures must change as the > requirements of the system change. The trick to managing that change is to > keep the system as simple and flexible as possible. Robert C. Martin > (Agile Software Development, page 325)
Looking back at this quote today, it still rings very true.