In this episode, hosts Karei and Mari explore the psychological tendencies that lead us to make predictably irrational decisions. Drawing on concepts from the book Predictably Irrational, the duo discusses the IKEA effect—the tendency to overvalue products we have built ourselves—and the sunk cost effect, which explains why we struggle to let go of projects or experiences after investing time or money into them. Through survey data and relatable examples, they examine how emotional attachment and the fear of wastefulness (In Japanese: "mottainai") often override objective logic in our daily lives