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.
I have a running joke that one of the most useful things I do when coaching or consulting is to say to people “Yes, that does sound like a problem. Have you tried solving it?”
Part of why this is a joke is that actually most of the useful work happens prior to the point - the hard part is actually articulating what is going wrong well enough that it seems like a soluble problem - but there is genuinely something useful about this, because often it feels people are looking for permission.
Without the external prompt, solving their problem is not something they noticed that they were allowed to do.