The Things You Buy Most Are the Ones You Misprice

Milk, instant noodles, eggs. You toss them in the cart every week — then someone asks the exact price and you freeze. You'd expect frequency to breed knowledge, but research says the opposite. Dickson and Sawyer's 1990 supermarket field study (Journal of Marketing) put it bluntly: shoppers who had just placed an item in their cart were asked its price on the spot, and nearly half couldn't give the right figure. The culprit is cognitive automation. Pricing out every purchase would burn too much mental energy, so the brain stores a single rough reference price for frequently bought items and stops actually reading the tag. The trap: that reference price is frozen at the moment it was first imprinted.

So the "was this always this expensive?" jolt usually isn't a sudden price spike — it's that your internal benchmark is anchored to a price from three years ago. Anchoring, first reported by Tversky and Kahneman in Science (1974), has been replicated in hundreds of studies, and even an upfront warning cuts the effect by only about 27%, leaving 70%-plus fully intact (Wilson et al. 1996). The gap between "I know prices" confidence and real accuracy is wider than you'd like.

Inflation Doesn't Arrive All at Once — Which Is Exactly Why You Miss It

The real ringleader behind distorted price sense is cumulative inflation. Three percent a year is barely a blip in any single year. But compounded, prices climb about 1.23x over seven years and 1.34x over ten. Our heads can't do that multiplication intuitively. Small changes get waved off every time, then one day the price tag hands you the whole bill at once. Here's how 3% compounding drifts away from what you feel.

On top of that, prices ending in 9 (charm pricing) blur things further. In Anderson and Simester's 2003 experiment, the same item sold 8% better at $39 than at $34 — the higher price moved more units. That's the left-digit effect. A brain seeing 19,900 won files it as "ten-thousand-something" and tosses the trailing digits. As Thomas and Morwitz showed with fMRI in 2005, the price-processing region reactivates only when the left digit changes; the right-end digits get largely ignored. So 19,900 won and 20,100 won differ by a mere 200 won, yet your head stores them a full "tier" apart.

The Trap of Skipping Unit Price

Another structural error is unit-price neglect. Same detergent, 8,900 won for 1.5L versus 13,900 won for 2.5L — who can say on the spot which is cheaper? Almost nobody. It takes converting to price per mL, and to dodge that 30-second calculation people lean on the heuristic that "bigger is always cheaper." In reality, bundles and large sizes are often the pricier deal. When Consumer Reports dug into 200 US cable and internet bundles in 2019, 41% of the advertised "bundle discounts" cost more than buying the items separately. The harder a price tag makes comparison, the better it guards its margin.

✍️ Operator's note — Every time I caught myself at the store thinking "was this always this expensive?" I blamed inflation — but when I actually checked, prices mostly hadn't spiked; my memory had just parked itself at the old prices. So these days I try to refresh my mental reference price for at least a few frequently bought items once a year. Keep reflexively saying "it used to be a thousand won," and you never learn what the right price is now.

How This Game Builds the Skill

The shopping price quiz is a tool that forces your internal reference price to slam into current market rates. Every question spits out, as a number, the distance between your stored anchor and the real answer — so you can see at a glance which categories your memory froze years back. When you estimate, don't get jerked around by the trailing digits; lock the left digit first (ten-thousands or hundred-thousands), and for large-size items run a quick mental conversion to unit price before you answer. With repetition, the vague "roughly this much" feeling gives way to a habit of recalibrating current market rates category by category.