A sunk cost fallacy is a fallacy where someone convinces themselves that they should continue doing something because they put in a lot of time and/or effort into it, even if they actually get very little reward out of it. For example, a person might watch the first six episodes of "Battlestar Galactica", but decides they do not like the show. However, because there was a sunk cost, six hours of time, that person tells themselves that because they already spent so much time on it, they might as well finish the show.