Prada stores carry a few obscenely expensive items in order to boost sales for everything else (which look like bargains in comparison). People used to download music for free, then Steve Jobs convinced them to pay. How? By charging 99 cents. That price has a hypnotic effect: the profit margin of the 99 Cents Only store is twice that of Wal-Mart. Why do text messages cost money, while e-mails are free? Why do jars of peanut butter keep getting smaller...