One "wins" a role-playing game by beating the other characters (preferably into unconsciousness).

You can "win" a tabletop by successfully getting to the end of the campaign, but that's about it. Of course, the players "win" by having fun. Unless the player trying to "win" is the sort of person that has the most fun messing it up for other people. In which case, resort to the first statement, but substitute "character" with "player".