The hardest part to understand in any complex system where human behavior plays a part is the human. And that's the part that's invariably over simplified in finance and economics. There's very little "human factor" in economics, except perhaps in the sub-field of behavioral economics.
As a voice user interface designer, I see it all the time. Project teams spend a great deal of time on the technology itself, because the technology is pretty difficult to implement. Unfortunately, the behavior of customers and callers and customer service reps is often given short shrift. That's too bad, because that's the really hard part to understand, and the success of an implementation is dependent on understanding and designing to accomodate the human part of the system.