A further comment about inhabiting the
inner mental life of one's character, as a player (building on my post 2016 upthread).
It relates to what
@Bedrockgames has said about "mental models", and what
@prabe has said about spontaneous production of fiction.
When, as a player of a character who is trained in the lore of the great masters and who is intent on finding spellbooks to enhance her repertoire of magic, I think
Isn't Evard's tower around here, I am engaging in the same mental process as the GM who, in response to a question from a player, feels that there is no logical or possible answer but
this is how things are in the gameworld.
In my view both are acts of authorship. But to the extent that someone is hesitant to use that word, because it doesn't
feel like making things up, then that is as true for the player playing the character as the GM "playing" the world.