Jake has plans to go to an opera and already has a $100 nonrefundable, nonexchangeable, and nontransferable ticket. Now Megan, whom Jake has wanted to date for a long time, asks him to a concert. Jake would prefer to go to the concert with Megan and forgo the opera, but he doesn't want to waste the $100 he spent on the opera ticket. From the perspective of an economist, if Jake decides to go to the opera, what has he just done