Say we encounter something we’ve always wanted. Let’s call it a widget (a common term in traditional economics textbooks representing a generic product designed both to obscure the fact that it has questionable value and to torment readers of traditional economics textbooks). Our widget is on sales! Fifty per cent off! Exciting, right? But stop for a second. Why do we care about the sale? Why do we care about what it used to cost? It shouldn’t matter what the cost was in the past since that’s not what it cast now. But because we have no way of really knowing how much this precious widget is worth, we compare the price now to the price before the sale (called the “regular” price), and take that as an indicator of its high current amazing value.