Why a worse third option can change the choice
Suppose a café offers a small coffee for $3 and a larger one for $4. Add a $3.80 coffee that is smaller than the $4 option. The new drink is worse than the larger coffee on both relevant dimensions: it costs almost as much and gives you less. That makes the $4 coffee look like a better deal than it did before.
This is called the decoy effect, or asymmetric dominance. The third option is “asymmetrically” dominated because the larger coffee clearly beats it, while the decoy does not necessarily make the $3 coffee look worse. The decoy therefore gives one of the original choices a comparison advantage.
The mind compares, not just calculates
People often judge value by comparing nearby options rather than working out an ideal price for each one in isolation. Before the decoy appears, the $3 coffee may seem like the sensible choice: it costs less, and the extra size may not feel worth another dollar. Once the $3.80 option is on the menu, the $4 coffee’s extra size is easier to notice because it comes at only a small additional cost over the decoy.
The decoy does not make the larger coffee objectively cheaper. It changes the reference point—the option against which the larger one is being judged. That comparison can make a previously uncertain trade-off feel obvious.
Why the effect has limits
A decoy works best when the options can be compared on clear, shared features, such as price and size. If buyers care more about taste, freshness, or how much coffee they actually want, those considerations may matter more than the menu’s carefully arranged price ladder. The effect can also depend on whether the difference between options is easy to understand.
For a seller, the practical lesson is that adding an option can influence choices even when few people buy it. The $3.80 coffee may earn little on its own; its job is to make the $4 coffee easier to choose.
