For the most part, people buy Coca Cola because of the image that the brand of soda projects. They feel that Coke is a product that is used by “cool” people or by people who are in some way admirable. For this reason, they buy Coke when there are any number of other products that could quench their thirst just as well.
Brands like Coke need to engage in marketing that differentiates their product from others. While there are differences in taste between Coke and other drinks, this is not what drives much of the demand for Coke and this is not what Coke focuses on in its advertising. Instead, Coke tries to project an image. People who buy Coke are fun people. They are active. They are cool. Thus, by buying Coke, consumers are in some sense identifying themselves with those attributes.
Thus, Coke is not really bought because of the way it tastes. Instead, it is bought for the image that it projects and the image that people who buy Coke want to project of themselves.