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’s chocolate at the supermarket, and you can get to the supermarket by driving, and driving requires that you be in the car, which means opening your car door, which needs keys. If you find there’s no chocolate at the supermarket, you won’t stand around opening and slamming your car door because the car door still needs opening. I rarely notice people losing track of plans they devised themselves.
It’s another matter when incentives must flow through large organizations—or worse, many different organizations and interest groups, some of them governmental. Then you see behaviors that would mark literal insanity, if they were born from a single mind. Someone gets paid every time they open a car door, because that’s what’s measurable; and this person doesn’t care whether the driver ever gets paid for arriving at the supermarket, let alone whether the buyer purchases the chocolate, or whether the eater is happy or starving.