Over on Story Games, I read a thread about a game designer lamenting that his playtesters were over competitive in his game. Of course they were! His game has a victory condition.
If your game has one of those, it will be about winning. People will play to win.
Not everyone will, of course. I have a friend Vince, who roleplays every game. Even Carcassone. He’ll be the “thieves” and focus on getting funky shaped roads, or whatever. He enjoys this more than trying to get the best score he can. Whatever floats his boat, right? But I think most people play board games to win, and when presented with an roleplaying game that can be ‘won,’ explicitly, they’ll act the same way.
Don’t want your game to be about winning? Don’t have a victory mechanic. End of story. It’s that simple.
Some games it detracts from more than others. 1001 Nights is a game that really should involve each player telling one story. The scoring works sort of as a pacing mechanic to see how long the individual stories end up being, but can make a player win before everyone’s gotten a chance to tell a story (and likely will do so in a larger game; it did when we played with three).
However, the premise of 1001 Nights and feel is so strong that it’s hard to get detracted from playing in character (and it’s hard to min-max your storytelling) This is an example of a game where the presence of a victory condition only holds back it’s potential rather than ruining it; the creeping influence of ‘how do I win’ is minimal and only occurs between stories.