Who knows more about the life in a pond – a fish that lives there or an ichthyologist who researches it?

When I work with companies working in B2B markets, I often hear from their executives that they don’t need customer research.
‘We have been working in this domain for years, so we know our customers very well,’ they say.
But one may spend their whole life working with clients but still learn little about them. A large volume of collected information doesn’t indicate high data quality.
I love a metaphor that conveys the idea very well.
So, who knows more about life in a pond – a fish or an ichthyologist?
The volume of information the fish has is large – it is inside the situation.
But I wouldn’t rely on its data when making decisions. I’d prefer the information provided by the ichthyologist because it is structured.
Many industrial experts are the ‘fish’ if they don’t use analytics, ad-hog studies, or customer research to inform their decisions…