A cognitive bias in behavioral economics, where individuals place a higher value on an object they own than an identical object they do not own. This is due to loss aversion and emotional attachment, and the effort of buying the same product again if it is lost. This can also be one reason why “Free trial!” exists, where quitting it seems like a loss, even though you don't lose any money. This is sometimes a mistake, even if sentimental; if something has no special use, it might be a good idea to sell it.
For instance, in RPGs, losing a videogame character in the story they already own feels worse than never having it in the first place.
Also, property is famous for this bias: territorialism. People assign their own chair in classrooms and workplaces instinctively. People may be mad if others make them "lose their spot".