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.
Imagine a circle that contains all of human knowledge.
By the time you finish elementary school, you know a little.
By the time you finish high school, you know a bit more.
With a bachelor's degree, you gain a specialty.
A master's degree deepens that specialty:
Reading research papers takes you to the edge of human knowledge.
Once you're at the boundary, you focus.
You push at the boundary for a few years.
Until one day, the boundary gives way.
And, that dent you've made is called a Ph.D..
Of course, the world looks different to you now.
So, don't forget the bigger picture.
Keep pushing.