How many times have you gone into Tesco or Sainsburys and bought something you didn't plan to (or sometimes even something you didn't need), just because they was a special promotion on such as buy one, get one free?

How many times have you bought three items, when you only needed one, simply because there was a  for the price of 2 offer on in the shop.

Everybody loves a bargain.

With the example I gave, you probably wouldn't have bought any of the items (since you didn't need them at the time) if there wasn't a promotion on.