自分で組み立てた箱は、なぜか高く見える。完成品より約6割高い値段がついた「IKEA効果」

Do you love things you made yourself? Scientists call this the IKEA effect. In one experiment, some people built a storage box by themselves. Other people just looked at the same box already built.

The builders said they would pay about 63 percent more for it. In another test, people valued their own paper cranes and frogs like an expert's work. But when people did not finish building, the effect disappeared.

Why does a shelf you built yourself seem better than one from a store? In 2012, researchers Michael Norton, Daniel Mochon and Dan Ariely named this the IKEA effect. In their experiment, some participants assembled a storage box, while others were shown an identical box that was already built. When asked how much they would pay, the builders offered about 63 percent more on average.

In another study, people who folded origami valued their own work almost as highly as an expert's, but other people valued it much lower. The effect disappeared, though, when people stopped before finishing or took apart what they had made. This suggests that the feeling of completing a task is the key.

After an evening spent wrestling with a flat-pack bookcase, people often feel oddly fond of the result. In 2012, Michael Norton, Daniel Mochon and Dan Ariely named this the IKEA effect. In one experiment, participants who built a storage box themselves were willing to pay about 63 percent more for it than people who judged an identical ready-made box.

In another, amateurs who folded origami valued their creations almost as highly as pieces made by experts, while outsiders found them clumsy and priced them far lower. The effect disappeared when people had to stop before finishing or take apart what they had built.

So it is successful completion, and not effort alone, that inflates the value. The phenomenon is related to effort justification, shown in a classic 1959 study in which people who went through an embarrassing initiation rated a dull group discussion as more interesting. A 2018 study suggests the bias appears in children around age five. The IKEA effect has upsides, such as greater satisfaction with homemade gifts. It also makes it hard to judge our own work objectively, and it may lead us to cling to failing plans because we put so much into them.