The story is what happens. The game is also what happens. The writer decides action in the story, but the player decides action in the game. Most games allow these to overlap. This is difficult because the story must encompass all possible player actions and motivations. This is important!
The story must encompass all possible player actions and motivations!
The player and the story must always be in complete harmony. The problem occurs when the game developer writes a story in conflict with the player. If they conflict then either the story wins or the player wins. If the story wins the player is no longer playing. Itís not a game anymore, just a movie, or even a book. If the player wins, then the story makes no sense. Itís not a story anymore, just a stupid sequence of disconnected actions. When they disagree the player either derails the story, or the story derails the play.