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.
Recall that great line from Umberto Eco’s novel The Name of the Rose
How beautiful the world would be if there were a procedure for moving through labyrinths.
Only, here, it’s some lonely postal worker—or a geography Ph.D. driven mad by student debt—out mapping the frayed edges of the world, wearily noting every new dead-end and cul-de-sac in a gridded notebook, diagramming loops, sketching labyrinths and mazes, driving empty streets all day on a quest for something undefinable, some answer to why the world’s patterns have gone so wrong. A self-diverging world, where things only almost meet.