When you’re designing a piece of custom software, in theory, your client tells you what he wants, and then you go and tell the computer how to give it to him. In reality, your client will never tell you what he actually wants, usually because he himself doesn’t actually know. But that’s okay, because he will most assuredly change his mind anyhow, as soon as you figure out how to do what you thought he asked for in the first place.

In other words, you’re trying to write something that you really don’t understand and that keeps changing from under your feet… kind of like writing a novel.