The idea that every decision we make has an opportunity cost is fundamental to economic theory, but at the same time it seems to be difficult for many people who have not been exposed to economics to fully comprehend. The fact that people ignore the opportunity cost of keeping an unwanted Christmas gift seems to suggest that people are irrational, or that economists are unable to measure all of the factors that go into an individual’s decision making. In my opinion, it is probably a mixture of both.
When someone receives an unwanted gift, which I’ll define as one that they would never purchase themselves, the “economically efficient” thing to do would be to sell the gift at the market price. It would seem irrational for a person not to sell the unwanted gift at the market price because they are incurring an opportunity cost equal to the market price of the gift by keeping it. However, the fact that most people probably do not return every unwanted gift might suggest that there are other factors to consider in addition to monetary opportunity costs. Perhaps there are opportunity costs greater than the cost of the gift, such as the cost of offending the gift giver, that economists are unable to measure and therefore might mistakenly identify as irrational behavior.