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.
There is a story of Rikyu which well illustrates the ideas of cleanliness entertained by the tea masters. Rikyu was watching his son Shoan as he swept and watered the garden path. "Not clean enough," said Rikyu, when Shoan had finished his task, and bade him try again. After a weary hour the son turned to Rikyu: "Father, there is nothing more to be done. The steps have been washed for the third time, the stone lanterns and the trees are well sprinkled with water, moss and lichens are shining with a fresh verdure; not a twig, not a leaf have I left on the ground"
"Young fool," chided the tea master, "that is not the way a garden path should be swept. "Saying this, Rikyu stepped into the garden, shook a tree and scattered over the garden gold and crimson leaves, scraps of the brocade of autumn! What Rikvu demanded was not cleanliness alone, but the beautiful and the natural also.