"But that doesn't happen very often."
It's often said with an awkward expression or laugh. This is the critical moment. Behind those non-committal words the user is really thinking--"These are details. This is my world. Does this geek care about my world? No, of course not." Of course behind our geeky glasses and awkward social graces we care a great deal about the user's world. The detail of the user's world is critical. Without detail there can be no accurate design. If the design is flawed then everything else will be broken too.
My response is typically like this:
"Often it's those things that don't happen very often that cause the most trouble. If you don't mind let's dig into this a bit more?"
I have never talked to anyone who was't thrilled to go into great detail once they felt that they had "permission" to get into the details.
