>It's not just that the business needs change - it's that many clients are simply unable to state all their business requirements and rules in one shot (even if that shot is done over weeks or even months). I sometimes find that client's rules are so 'patched' that a full-blown discovery process uncovers the fact that clients have been inconsistent in their own rules. So sometimes buiding a brand new system uncovers so many of these, that the system becomes a "proof of concept" for their rules. And that process sure as heck can't be neatly determined on some bean-counter's ledger! ;)

And worse than that,it is often a proof of concept that their rules don't make much sense, that there's no overall logic, just a set set of reactions to common situations. When an analyst comes in and tries to put the picture together, there are a lot of pieces of the puzzle not just missing, but never existed.

Another thing that usually emerges is the story behind a "we have ALWAYS done it THIS WAY" rule. There's a history of a strong boss who invented a rule to prevent some common screwups which were happening in his time. He's long retired, and nobody remembers the reason for the rule, they all just blindly adhere to it (and occasionally get bad rap for violating it). And now his heirs are trying to push that rule into the project, but can't explain it.