But we weren't talking about the play at the table, where such a distinction might be necessary. We were talking about pemerton who apparently gets confused by the words PC and player, or the idea that other people understand that things aren't happening in real life.
<snip>
There's a game world. The GM describes it. Maybe the PCs also describe it. That description has meaning to the PCs, helps to inform their actions, and thus helps to further define the game world.
Many RPGs - Burning Wheel, Apocalypse World, Classic Traveller (1977 version), and others - rely on the fact that (i) a dice roll is something that can be done at the table by a player, as a result of them declaring an action for their PC, and (ii) can then trigger (due to its result, which feeds into the rules of the game) some narration by a GM, without (iii) the in-fiction cause of whatever elements the GM mentions being the PC under the control of that player.
The interplay of (i), (ii) and (iii) is what makes it possible for
the player to never have to do anything but declare actions for their PC yet
the stuff the GM narrates is highly constrained by the player's concerns for their PC (ie the PC's dramatic needs).
If, as a matter of principle, you won't accept that "player" and "PC" are words that refer to different things, then I can't explain the above to you, because you will insist (for instance) that the PC is the author of their own dramatic needs, that the rolling of the dice and the result they produce is something the PC is doing in the fiction, etc.
If you want to insist on the stuff in the previous paragraph being axiomatic, OK, knock yourself out! But it will mean that you can't understand the vast swathes of RPGing for which it is not axiomatic.
EDIT: In the first LotR film, Peter Jackson lets the audience know that there is a Hobbit called Farmer Maggot because Frodo says to Merry and Pippin something to the effect of "You've been in Farmer Maggot's fields again!"
Novels often use the same device: eg in one of the Le Carre novels about George Smiley, the way the reader comes to know that Smiley has a wife called Anne is that one of the other characters asks Smiley "How's Anne?"
A story which introduces every element by direct narration rather than this sort of obliqueness - "There once was a Hobbit called Farmer Maggot", "There once was a spy called George Smiley who had a wife called Anne" - will come across as rather child-like in its narrative style.
The (i), (ii), (iii) technique I've described above is the RPG analogue of the sort of obliqueness I've just described: it allows fictional elements to be brought into play without anyone having to directly narrate them. This is why, upthread, I said that Gygax and Arneson probably did it too, even though I don't think they wrote it down as a technique: it's an obvious and powerful tool.