[Retric]

I always liked:

Your supposed to design a 4 lane bridge for a new interstate, you say sure that takes 6 months where do you want it?. After 3 months they decide where they want it and expect the design in 3 more months. You say, that's not going to happen I might be able to pull 5 months though.

So, assuming you know where it's going to be you start pulling in some overtime and get to work. After another month they say, we need a 6 lane bridge, after another they want to add a train. And 2 weeks before the deadline they decide on a tunnel. SO, you end up submitting a 6 lane bridge design that can't handle trains.

Which is why software is always late, and you don't hand them what they want.

[drbawb]

I like this analogy as well as the analogy you replied to simply because they relay the massive velocity of change we have to face.