The reasoning here is the same that applies to all moves, in all PbtA games, all the time... do you have the appropriate Fictional Positioning to do that?
If yes, then your example (as extreme as it may seem out of context) will make perfect sense for everyone at the table within the specific circumstances.
If not, then the move does not trigger and the World makes a judgement call.
So if the table feels that it lies within the realm of possibility that what a PC is saying to the King might actually have a chance of convincing him to do whatever... THEN the move triggers and you go through with its instructions:
1) is the Player's description of their PC's actions triggering the move? Or do they need to describe something more/less/different for it to be the move?
2) is the NPC already convinced by the words and actions of the PC? Or are they doubtful/resisting/etc?
3) profit :P
- - -
If something feels POSSIBLE and/or PLAUSIBLE to the group, THEN the move deals with the chances of it being pulled off or not, and with which consequences.
Otherwise, it just can't be done... not at all... or maybe just not like this...
Does this answers your question? :)
The revised text will actually have a whole section explicitly explaining Fictional Positioning in practical terms, and with specific regards to moves, addressing a lot of questions I collected in these years of play :)