Margot has fallen in love with a three-bedroom, 2,500-square-foot property in her friend’s neighborhood. It’s listed for $400,000. However, just down the street, another three-bedroom, 2,400-square-foot home very similar to the one Margot loves was just listed for $350,000. Margot and her agent immediately make an offer on the second property. Which economic principle is at work here?