Coke- the more you have on hand, the more you consume.
Toiletpaper- you'll pretty much use the same no matter how much you have.
So when you discount a Toiletpaper product, people will stockpile it. They won't ever pay full price because they'll always buy on sale and have what they need.
For Coke, you can discount and people will buy a lot, but it will serve to make them more regular drinkers. This should actually increase loyalty.
(I learned this today in BYU's MBA 550 "Marketing Management") I suppose it applies more consumer products. Kind of funny.