the major problem for coke, page-18

In actual fact a lot of products taste better than coke (such as Pepsi) but coke has a wired physiologic al effect on the brain that causes people to feel happier when drinking coke. Many associate this with their advertising and branding. The dissipation of coke for cheaper products has happened in the past but it is typically only temporary in duration with the exception of an occasional product such as red bull (impression expensive) that maintains market share.

Admittedly disposable income reductions over a long period result in a decreased coke consumption across the board and vice versa.