There's a lot of discussion about what a game is, in the context of RPGs, and even when I propose an answer, I never imagine it to be the only answer. Still, it's interesting to think about.
I was chewing on that today and considered a slightly different approach - a game (or rather, the act of play at any given moment) is an *argument* about how things should turn out. I suppose it might be nice to call it a negotiation, but I think argument is a better word since positions tend to be put forward forcefully and while there may be movement towards compromise, that is far from a necessity.
The important and potentially powerful point to this perspective is that it suggests that individual perspectives on what a game is become arguments within that context. To illustrate this idea consider that "Because it makes the best story" is a powerful argument, but it's not the only argument.
More familiar arguments include the sort of things that might be described as crunchy minutiae, like how many inches of plywood a desert eagle can shoot through. You get similar issues with strongly held opinions about setting or character elements - "My Guy" syndrome falls under this, but all manner of setting and genre expertise matters fall under it as well. Turning to an external arbiter (like dice) is another kind of argument.
These arguments are almost certainly familiar to every gamer out there, and while some might characterize them as problematic arguments, but I am pretty confident that the real confusion stems from another source. It's not the arguments themselves that create a problem, it's the certainty associated with them. As in civil discussion, certainty creates all manner of problems in coming to resolution.
Now, every group has their own biases regarding what makes a good argument, and so long as the group is in agreement regarding what arguments are and aren't fair game, then things will probably go well, provided those expectations are looked at, thought about, and communicated well.
I admit my own bias is to bring as many arguments as possible to the table, though I obviously fall victim to my own tastes, often without realizing it. I admit it can make things more complicated, but I find a lot of benefit in apparent contradictions. And more, it can become habit - looking at every argument, every time can seem like a lot of work, but the more time you spend looking at different arguments, the more arrows you have in your quiver when it comes time to resolve things (either as a player or a GM).
Everway had a great method for this, explicitly calling out three arguments out as Karma (stats), Drama (needs of the plot/story) and Fortune (draw of the cards). It was a fantastic muscle-builder for me as a GM, and I absolutely encourage a GM to try something similar, if only to see how it helps thing think about things differently.