Rule 3: Good, Fast, Cheap - Pick Two
I didn't make up this rule. I borrowed it. This rule is an old Hollywood maxim. What it means is that there are three conditions that every moviemaker would like to have met when doing a film. Every producer wants a good film, made fast, and done cheaply. However, the rule says that you get only two of these features. If you make a good movie quickly, it won't be cheap. If you make a movie quickly and cheaply, it won't be good. If you want a movie that's good and cheap, it won't be quick to make.
The same is true for software. (In fact, the practice of making software has more in common with the practice of making movies than not.) It's important that the client understand this fact. The rule has been around for a long time, and has rarely proven wrong. If a client wants good software, made fast, and delivered cheap, walk away. The project is doomed from the beginning.