
As Waldfogel explains it on Planet Money, we only buy ourselves things that are worth their price to us (a $50 sweater that will give $50 worth of pleasure, for instance.) But all sorts of other variables come into play when the item is bought for a third party. If that present is a dud, and ends up in the closet, it represents a complete (100%) waste of resources. And the chances that the present will be unwanted, or be worth far less than its monetary value to the recipient, are unacceptably high for a guy whose life's work is cost-benefit analysis.
Another argument for re-gifting?