Once you see that an answer is not serving its question properly anymore, it should be tossed away. It's just their natural life cycle.
They usually kick and scream, raising one hell of a ruckus when we ask them to leave. Especially when they have been with us for a long time.
You see, too many actions have been based on those answers. Too much work and energy invested on them. They feel so important, so full of themselves. They will answer to no one. Not even to their initial question!
The hardest thing about customer interviews is knowing where to dig. An effective interview is more like a friendly interrogation. We don’t want to learn what customers think about the product, or what they like or dislike — we want to know what happened and how they chose... To get those answers we can’t just ask surface questions, we have to keep digging back behind the answers to find out what really happened.
In my opinion, what makes a designer competent is precisely their ability to credibly justify their conclusions. If you can’t do this as a designer—no matter how successful your results are—then neither I nor anybody else can tell if you aren’t just picking things at random.
What I am proposing, then, is no less than to make a designer’s entire line of reasoning a matter of permanent record. On the surface is the familiar set of prescriptions, components, examples and tutorials, like you would expect out of any such artifact. Attached to every element, though, is a little button that says You click it, and it tells you. The proximate explanation will probably not be very satisfying, so you click on the next until you get to the end, at which point you are either satisfied with the explanation, or you aren’t.