A lot of illusionism - or advocacy for illusionism - seems to rest on a premise that all the "engine" for play has to come from the GM.
That can be the case, but it doesn't have to be the case.
Yes, this is true: The GM is the Engine of the whole Game Word. It's really a basic part of being a GM. There is no one else in the game to do it.
A player, in a traditional game where they only control their one character, can only...at best...make vague suggestions. And then the GM has to step in and do all the work and make the Engine go. For many players the "saying a random vague suggestion" every once in a while makes them "feel good", so a lot of GMs just let this slide.
In the traditional game the GM makes up a lot of stuff before the player even encounters it: making at least a rough adventure framework. And maybe most of all a reality based, sane world that 'works'. A GM can make nothing, let the player make their vague suggestions, and then just improv the world right in front of the player. Though this really puts the burden of creation on the player, and they maybe unwilling or unable to handle it. The player is often unwilling or unable to keep track of created things, so they will just randomly create things on their whims. This can make for a crazy, unrealistic mess of a world. Unless the GM steps in to fix every mistake a player makes: it would just be easier for the GM to create everything with rational, common sense.
But even if you do the above, once your immersed in a single plot story, the GM really has to be the Game Engine. The plot and story must move forward in a game based on reality. If you don't, your playing the worst version of some of the worst video games ever: no matter what the PC does Everything resets to default as soon as they leave an area.
This is where I am. I don't believe I railroad players, rather I set up the situation, I know exactly what's going to happen if the player's don't interfere, and I leave them free to decide how best to handle things. Like I said earlier in the thread, it's only railroading if you don't allow players to make meaningful choices. If I want to introduce an adventure hook, it's necessary for me to contrive a situation where it's introduced. Instead of ogres, maybe it's a merchant with a broken wagon. It doesn't matter which direction the PCs go in, they're going to encounter this merchant, but it's up to them what they do at this point.
I know Railroading has a "bad name", and I'm trying to change it. Like most things it can be used for good and bad.
A lot of things in a game the players "have" to do with no choice. If the players want to destroy the undead of the lost ruins....well, then they have to take some sort of directed action towards that goal.
And while some things to have more then one way or "path" you can take towards a goal.....really like more then half of the time the pathway is really just a simple straightforward one. The players want to destroy the undead of the lost ruins: they go to the ruins and attack and destroy the undead in combat. While there are other paths, most often they are not open to the characters. A Wave of Holy Water could destroy all the undead....but the PCs can't summon 100 billion gallons of holy water anyway.
You would think so, but I've had occasion to see my players avoid encounters and plot hooks during campaigns and even strangers at one-shots at my local gaming store.
It's normal enough for players with characters "on a mission/quest" to ignore side things. Really a DM should avoid such things.
If, for example, you opened the session with the scene with the merchant, would that somehow count as illusionism or railroading, as opposed to if you had it happened 10 minutes into the session?
This does make my point that: Things Must Happen. The fictional game world in a simulation must move, live and breathe to feel real. If not your left with the video game world where NPC X just "says" to the PCs some boxed text any time the PCs get within five feet of him.
Again, it's exactly like the fiction in media: no matter what bar the hero goes to, the bad guys will be there waiting so there can be a cool bar fight scene. This is 100% fake and an illusion and a railroad: but it MUST happen. The fight scene at the bar is a cool action scene....and it's the type of thing people watching the action movie WANT to see. So the "movie logic" makes it happen, and no one in the movie questions it in-universe.