I don't think this addresses
@chaochou's point.
(1) He is not talking about
what happens to the PCs in the fiction. He is talking about what happens at the table.
(2) At the table, he is not talking about the agency of the players to speak words like
I try such-and-such. He is talking about the agency of the players to
actually change the shared fiction by having their PCs do things. If the GM decrees that a change can't take place because such-and-such is impossible, the player has not exercised any agency. Their attempt at the exercise of agency has been blocked/negated by the GM.