Studies have found that we irrationally over-value objects we make ourselves. The details:
[W]e don’t love everything we make equally. First, the labor has to be hard enough to really make us feel that we’ve put some sweat equity into the project. When making things ourselves is too easy—say, screwing a light bulb into a new lamp—people do not come to overvalue their creations. On the other end of the spectrum, tasks that are too difficult—such that we can’t even finish them—lead to frustration and disappointment (and, let’s be honest, swearing), which also undercuts the value we place on our creations.