The Endowment Effect is a phenomenon in behavioral economics that suggests that people ascribe more value to something simply because they own it. This effect is often seen in situations where people are unwilling to part with an item even when offered a fair price for it. This effect can be seen in both
From Wikipedia
In psychology and behavioral economics, the endowment effect, also known as divestiture aversion, is the finding that people are more likely to retain an object they own than acquire that same object when they do not own it. The endowment theory can be defined as "an application of prospect theory positing that loss aversion associated with ownership explains observed exchange asymmetries."