I like the mercury metaphor. Here's a another one for Agile.: Don't build a stone fortress for a nomadic tribe. If someone wants to give you a full specificati

I like the mercury metaphor. Here's a another one for Agile.: Don't build a stone fortress for a nomadic tribe. If someone wants to give you a full specification and stick to it, you can build something fully specified. If they give you a vague idea that will change a lot, build them as little as necessary and make it flexible enough to change with the idea. If your code's going along for the trip, it may as well be easy to pack.