How do you think "New Coke" happened? Malcolm Gladwell has the details in one of his books. You remember back when Pepsi used to do those taste test ads saying more people preferred Pepsi? Coke repeated the tests internally and found they were right (barely).
So Coke decided to reformulate. Pepsi is sweeter than Coke, so that is what Coke did. They repeated their taste tests, got good results and told the whole world.
Where they had screwed up is that they used small containers for their latter taste tests. People are quite happy for sweetness in small quantities, but as the volume of drink gets larger they prefer less sweetness "density". Naturally the new Coke was far too sweet and there was the resultant backlash.
TL/DR: A major contributor to Coke messing up "New" Coke was using too small testing cups.
So Coke decided to reformulate. Pepsi is sweeter than Coke, so that is what Coke did. They repeated their taste tests, got good results and told the whole world.
Where they had screwed up is that they used small containers for their latter taste tests. People are quite happy for sweetness in small quantities, but as the volume of drink gets larger they prefer less sweetness "density". Naturally the new Coke was far too sweet and there was the resultant backlash.
TL/DR: A major contributor to Coke messing up "New" Coke was using too small testing cups.