Endowment Effect

The endowment effect (also known as divestiture aversion) is the human tendency to attribute more value to their own possessions than they attribute to the possessions of others. You can easily see this in young children who have no problem with damaging or destroying other children's belongings while not sharing or being highly protective of their own possessions. A common laboratory example shows that people will pay more to keep an item they own rather than to receive something they don't own - this occurs even when they just received the item and they have absolutely no attachment to it.