TLDR: McDonald's customers buy milkshakes. Marketing people ask customers how they can make milkshakes better... to sell more. They make changes with zero change in sales.
A researcher asks people who buy milkshakes: what is the job that the shake fills for you? Why do you "hire" the shake?
Answer: early morning commuters want something to eat while driving to work. A shake isn't a good breakfast, but it's quick and easy to buy then consume while driving to work. Satisfying.
The point is making a shake "better" won't help anyone! "How can we make it better" is the wrong question!
https://www.youtube.com/watch?v=Stc0beAxavY
I included this video in a onboarding guide for my team and many enjoyed it.