Free-To-Play games are becoming increasingly popular as a business model for video games.  The problem with these games is that often players develop addictive behaviors while playing these games.  Since money is no longer an entry point the game is much easier to start playing. But now the time becomes the prime currency for enjoyment with that game.  Players are encouraged to continue playing for hours on end in order to unlock, usually meaningless, virtual content.  Then players find it hard to quit a game after they have made such a large time commitment to that game.  Players feel a need to make their time use worthwhile so they continue playing to reach their next goal.