The good that people buy MORE of when it gets pricier

One of the first rules you learn in economics is the law of demand: when a price goes up, people buy less. But a rare category called a Giffen good flips this on its head — when its price rises, people buy more of it. For over a century this was a textbook curiosity with almost no confirmed real-world example.

The trick is that a Giffen good is a cheap staple that dominates a poor household's budget — think plain rice or bread. When rice gets more expensive, a poor family can no longer afford the occasional meat or vegetables that round out their meals. To avoid going hungry, they cut the luxuries and buy even more of the cheap, filling staple. The price went up, yet consumption went up too.

Economists Robert Jensen and Nolan Miller finally documented this in a 2008 field experiment in China's Hunan and Gansu provinces, where subsidizing (lowering) the price of rice and wheat actually made poor families buy less of it. The effect only appears at the edge of subsistence — which is exactly why it's so rare and so hard to catch in the wild.