The sign says BUY 2 GET 1 FREE. Your brain hears “free” before it checks whether buying three costs less than buying one.
That is the framing effect: the same choice can feel different when it is presented as a gain, a discount, or a loss. Tversky and Kahneman’s original study found that changing the wording of a decision can shift preferences even when the underlying outcomes stay the same. 1
In the aisle, the resistance move is simple: cover the promotional headline and compare the unit price.