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.
Picture a blind man probing his way with a cane. While he is alert to the feelings in the hand holding the cane, the crucial distinction may be defined by saying that these feelings are not watched in themselves, but that he watches something else by way of them, that is, by keeping aware of them. He has a subsidiary awareness of the feelings in his hand, feelings which are merged into a focal awareness at the end of the cane, constituting two kinds of awareness that are mutually exclusive — "from awareness" and "focal awareness".
There is here a particularly interesting phenomenal transformation. The sensations of the cane on his hand (the surface of the cane as it touches the palm of his hand, etc.) are lost. Instead, he feels the end of the cane as it touches an object...If our blind man shifts his attention from the tip of his cane to his hand, the meaning on the end of the cane disappears.