How many times have you gone into a store and seen signs that say something along these lines: "Supplies running fast!" "Buy them before they're gone!" "Only 5 left!" "Sale ends soon!" Now, be honest: How many times did you go through with the purchase because you believed what the signage said to be true? Yep, even I've fallen for it myself, and I actually majored in marketing and minored in psychology! In marketing and consumer psychology, it's what we call the scarcity principle : Consumers attach more value to things that are few in quantity and thus feel more compelled to purchase such items. But this isn't limited to brick-and-mortar stores -- companies also use this marketing tactic online. Take Amazon.com. At some point, you're bound to come across an item whose description includes "Only 3 left in stock. Order soon." Companies seldom run out of inventory, unless we're talking about much...