Life would be so much simpler if our customer would just tell us exactly what they want the product to do. I wonder why they don’t just write it all down, then we can go off and build it?
In my experience, the customer can’t do this because they don’t know exactly what they want. They have a feel for what they would like, but they don’t always know what is technically feasible given the time & budget constraints. There’s almost always a trade-off between what they would like and what they can afford; maybe Feature A could be a little more robust if a couple of bells and whistles are dropped from Feature B, for example.