In one or two sentences, explain the link between economic wants and preferences

This expression relates to opportunity cost because even though there are things that are free in this world, saying "everything has a cost" is metaphorically true. For example, making a decision between two items and not choosing the best alternative means giving up your own happiness which isn't paid for by money, but your own decisions and making that decision to buy something that was not of your best personal interest in the end, that has costed you your satisfaction; this is a definition of opportunity cost. Therefore, that is how the expression and opportunity are linked.